add Message.post_message_view_type to jsonrpc api, to get the real viewtype of a pre-message.

fix python lint errors

receive pre-mesages, start with changes to imap loop.

refactor: move download code from `scheduler.rs` to `download.rs`, also
move `get_msg_id_by_rfc724_mid` to `MsgId::get_by_rfc724_mid`

`MAX_FETCH_MSG_SIZE` is no longer unused

Parse if it is a pre-message or full-message

start with receiving logic

get rid of `MsgId::get_by_rfc724_mid` because it was a duplicate of
`message::rfc724_mid_exists`

docs: add hint to `MimeMessage::from_bytes` stating that it has
side-effects.

receiving full message

send and receive `attachment_size` and set viewtype to text in
pre_message

metadata as struct in pre-message in header. And fill params that we can
already fill from the metadata. Also add a new api to check what
viewtype the message will have once downloaded.

api: jsonrpc: add `full_message_view_type` to `Message` and
`MessageInfo`

make PreMsgMetadata.to_header_value not consume self/PreMsgMetadata

add api to merge params

on download full message: merge new params into old params and remove
full-message metadata params

move tests to `src/tests/pre_messages.rs`

dynamically allocate test attachment bytes

fix detection of pre-messages. (it looked for the ChatFullMessageId
header in the unencrypted headers before)

fix setting dl state to avaiable on pre-messages

fix: save pre message with rfc724_mid of full message als disable
replacement for full messages

add some receiving tests and update test todo for premessage metadata

test: process full message before pre-message

test receive normal message

some serialization tests for PreMsgMetadata

remove outdated todo comment

test that pre-message contains message text

PreMsgMetadata: test_build_from_file_msg and test_build_from_file_msg

test: test_receive_pre_message_image

Test receiving the full message after receiving an edit after receiving
the pre-message

test_reaction_on_pre_message

test_full_download_after_trashed

test_webxdc_update_for_not_downloaded_instance

simplify fake webxdc generation in
test_webxdc_update_for_not_downloaded_instance

test_markseen_pre_msg

test_pre_msg_can_start_chat and test_full_msg_can_start_chat

test_download_later_keeps_message_order

test_chatlist_event_on_full_msg_download

fix download not working

log splitting into pre-message

add pre-message info to text when loading from db. this can be disabled
with config key `hide_pre_message_metadata_text` if ui wants to display
it in a prettier way.

update `download_limit` documentation

more logging: log size of pre and post messages

rename full message to Post-Message

split up the pre-message tests into multiple files

dedup test code by extracting code to create test messages into util
methods

remove post_message_view_type from api, now it is only used internally
for tests

remove `hide_pre_message_metadata_text` config option, as there
currently is no way to get the full message viewtype anymore

Update src/download.rs
resolve comment

use `parse_message_id` instead of removing `<>`parenthesis it manually

fix available_post_msgs gets no entries
handle forwarding and add a test for it.

convert comment to log warning event on unexpected download failure

add doc comment to `simple_imap_loop`

more logging

handle saving pre-message to self messages and test.

deltachat-ffi/deltachat.h

@@ -488,13 +488,15 @@ char*           dc_get_blobdir               (const dc_context_t* context);
  *                    0=use IMAP IDLE if the server supports it.
  *                    This is a developer option used for testing polling used as an IDLE fallback.
  * - `download_limit` = Messages up to this number of bytes are downloaded automatically.
- *                    For larger messages, only the header is downloaded and a placeholder is shown.
+ *                    For messages with large attachements, two messages are sent:
+ *                    a Pre-Message containing metadata and a Post-Message containing the attachment.
+ *                    Pre-Messages are always downloaded and show a placeholder message 
  *                    These messages can be downloaded fully using dc_download_full_msg() later.
- *                    The limit is compared against raw message sizes, including headers.
- *                    The actually used limit may be corrected
- *                    to not mess up with non-delivery-reports or read-receipts.
+ *                    Post-Messages are automatically downloaded if they are smaller than the download_limit.
  *                    0=no limit (default).
  *                    Changes affect future messages only.
+ * - `hide_pre_message_metadata_text` = Pre-Messages get information added to their text field.
+ *                    UI can set this to true when it already displays this information in a prettier manner.
  * - `protect_autocrypt` = Enable Header Protection for Autocrypt header.
  *                    This is an experimental option not compatible to other MUAs
  *                    and older Delta Chat versions.
@@ -4310,7 +4312,8 @@ char*             dc_msg_get_webxdc_info      (const dc_msg_t* msg);
 
 /**
  * Get the size of the file. Returns the size of the file associated with a
- * message, if applicable.
+ * message, if applicable. 
+ * If message is a pre-message, then this returns size of the to be downloaded file.
  *
  * Typically, this is used to show the size of document files, e.g. a PDF.
  *
@@ -7263,22 +7266,9 @@ void dc_event_unref(dc_event_t* event);
 /// `%1$s` will be replaced by the percentage used
 #define DC_STR_QUOTA_EXCEEDING_MSG_BODY   98
 
-/// "%1$s message"
-///
-/// Used as the message body when a message
-/// was not yet downloaded completely
-/// (dc_msg_get_download_state() is e.g. @ref DC_DOWNLOAD_AVAILABLE).
-///
-/// `%1$s` will be replaced by human-readable size (e.g. "1.2 MiB").
+/// @deprecated Deprecated 2025-11-12, this string is no longer needed.
 #define DC_STR_PARTIAL_DOWNLOAD_MSG_BODY  99
 
-/// "Download maximum available until %1$s"
-///
-/// Appended after some separator to @ref DC_STR_PARTIAL_DOWNLOAD_MSG_BODY.
-///
-/// `%1$s` will be replaced by human-readable date and time.
-#define DC_STR_DOWNLOAD_AVAILABILITY      100
-
 /// "Multi Device Synchronization"
 ///
 /// Used in subjects of outgoing sync messages.

deltachat-jsonrpc/src/api/types/message.rs

@@ -48,6 +48,9 @@ pub struct MessageObject {
     has_location: bool,
     has_html: bool,
     view_type: MessageViewtype,
+    /// If message is a Pre-Message,
+    /// then this returns the viewtype it will have when it is downloaded.
+    post_message_view_type: Option<MessageViewtype>,
     state: u32,
 
     /// An error text, if there is one.
@@ -92,6 +95,8 @@ pub struct MessageObject {
 
     file: Option<String>,
     file_mime: Option<String>,
+    /// Returns the size of the file in bytes, if applicable.
+    /// If message is a pre-message, then this returns size of the to be downloaded file.
     file_bytes: u64,
     file_name: Option<String>,
 
@@ -210,6 +215,7 @@ impl MessageObject {
             has_location: message.has_location(),
             has_html: message.has_html(),
             view_type: message.get_viewtype().into(),
+            post_message_view_type: message.get_post_message_viewtype().map(Into::into),
             state: message
                 .get_state()
                 .to_u32()
@@ -681,6 +687,9 @@ pub struct MessageInfo {
     rfc724_mid: String,
     server_urls: Vec<String>,
     hop_info: String,
+    /// If message is a Pre-Message,
+    /// then this returns the viewtype it will have when it is downloaded.
+    post_message_view_type: Option<MessageViewtype>,
 }
 
 impl MessageInfo {
@@ -704,6 +713,7 @@ impl MessageInfo {
             rfc724_mid: message.rfc724_mid().to_owned(),
             server_urls,
             hop_info,
+            post_message_view_type: message.get_post_message_viewtype().map(Into::into),
         })
     }
 }

deltachat-rpc-client/tests/test_chatlist_events.py

@@ -1,7 +1,5 @@
 from __future__ import annotations
 
-import base64
-import os
 from typing import TYPE_CHECKING
 
 from deltachat_rpc_client import Account, EventType, const
@@ -111,40 +109,6 @@ def test_delivery_status_failed(acfactory: ACFactory) -> None:
     assert failing_message.get_snapshot().state == const.MessageState.OUT_FAILED
 
 
-def test_download_on_demand(acfactory: ACFactory) -> None:
-    """
-    Test if download on demand emits chatlist update events.
-    This is only needed for last message in chat, but finding that out is too expensive, so it's always emitted
-    """
-    alice, bob = acfactory.get_online_accounts(2)
-
-    alice_contact_bob = alice.create_contact(bob, "Bob")
-    alice_chat_bob = alice_contact_bob.create_chat()
-    alice_chat_bob.send_text("hi")
-
-    alice.set_config("download_limit", "1")
-
-    msg = bob.wait_for_incoming_msg()
-    chat_id = msg.get_snapshot().chat_id
-    msg.get_snapshot().chat.accept()
-    bob.get_chat_by_id(chat_id).send_message(
-        "Hello World, this message is bigger than 5 bytes",
-        html=base64.b64encode(os.urandom(300000)).decode("utf-8"),
-    )
-
-    message = alice.wait_for_incoming_msg()
-    snapshot = message.get_snapshot()
-    assert snapshot.download_state == const.DownloadState.AVAILABLE
-
-    alice.clear_all_events()
-
-    snapshot = message.get_snapshot()
-    chat_id = snapshot.chat_id
-    alice._rpc.download_full_message(alice.id, message.id)
-
-    wait_for_chatlist_specific_item(alice, chat_id)
-
-
 def get_multi_account_test_setup(acfactory: ACFactory) -> [Account, Account, Account]:
     alice, bob = acfactory.get_online_accounts(2)
 

deltachat-rpc-client/tests/test_something.py

@@ -5,13 +5,12 @@ import logging
 import os
 import socket
 import subprocess
-import time
 from unittest.mock import MagicMock
 
 import pytest
 
-from deltachat_rpc_client import Contact, EventType, Message, events
-from deltachat_rpc_client.const import DownloadState, MessageState
+from deltachat_rpc_client import EventType, events
+from deltachat_rpc_client.const import MessageState
 from deltachat_rpc_client.pytestplugin import E2EE_INFO_MSGS
 from deltachat_rpc_client.rpc import JsonRpcError
 
@@ -336,7 +335,7 @@ def test_receive_imf_failure(acfactory) -> None:
     alice_contact_bob = alice.create_contact(bob, "Bob")
     alice_chat_bob = alice_contact_bob.create_chat()
 
-    bob.set_config("fail_on_receiving_full_msg", "1")
+    bob.set_config("simulate_receive_imf_error", "1")
     alice_chat_bob.send_text("Hello!")
     event = bob.wait_for_event(EventType.MSGS_CHANGED)
     assert event.chat_id == bob.get_device_chat().id
@@ -345,17 +344,16 @@ def test_receive_imf_failure(acfactory) -> None:
     snapshot = message.get_snapshot()
     assert (
         snapshot.text == "❌ Failed to receive a message:"
-        " Condition failed: `!context.get_config_bool(Config::FailOnReceivingFullMsg).await?`."
+        " Condition failed: `!context.get_config_bool(Config::SimulateReceiveImfError).await?`."
         " Please report this bug to delta@merlinux.eu or https://support.delta.chat/."
     )
 
     # The failed message doesn't break the IMAP loop.
-    bob.set_config("fail_on_receiving_full_msg", "0")
+    bob.set_config("simulate_receive_imf_error", "0")
     alice_chat_bob.send_text("Hello again!")
     message = bob.wait_for_incoming_msg()
     snapshot = message.get_snapshot()
     assert snapshot.text == "Hello again!"
-    assert snapshot.download_state == DownloadState.DONE
     assert snapshot.error is None
 
 
@@ -591,94 +589,6 @@ def test_mdn_doesnt_break_autocrypt(acfactory) -> None:
     assert snapshot.show_padlock
 
 
-def test_reaction_to_partially_fetched_msg(acfactory, tmp_path):
-    """See https://github.com/deltachat/deltachat-core-rust/issues/3688 "Partially downloaded
-    messages are received out of order".
-
-    If the Inbox contains X small messages followed by Y large messages followed by Z small
-    messages, Delta Chat first downloaded a batch of X+Z messages, and then a batch of Y messages.
-
-    This bug was discovered by @Simon-Laux while testing reactions PR #3644 and can be reproduced
-    with online test as follows:
-    - Bob enables download limit and goes offline.
-    - Alice sends a large message to Bob and reacts to this message with a thumbs-up.
-    - Bob goes online
-    - Bob first processes a reaction message and throws it away because there is no corresponding
-      message, then processes a partially downloaded message.
-    - As a result, Bob does not see a reaction
-    """
-    download_limit = 300000
-    ac1, ac2 = acfactory.get_online_accounts(2)
-    ac1_addr = ac1.get_config("addr")
-    chat = ac1.create_chat(ac2)
-    ac2.set_config("download_limit", str(download_limit))
-    ac2.stop_io()
-
-    logging.info("sending small+large messages from ac1 to ac2")
-    msgs = []
-    msgs.append(chat.send_text("hi"))
-    path = tmp_path / "large"
-    path.write_bytes(os.urandom(download_limit + 1))
-    msgs.append(chat.send_file(str(path)))
-    for m in msgs:
-        m.wait_until_delivered()
-
-    logging.info("sending a reaction to the large message from ac1 to ac2")
-    # TODO: Find the reason of an occasional message reordering on the server (so that the reaction
-    # has a lower UID than the previous message). W/a is to sleep for some time to let the reaction
-    # have a later INTERNALDATE.
-    time.sleep(1.1)
-    react_str = "\N{THUMBS UP SIGN}"
-    msgs.append(msgs[-1].send_reaction(react_str))
-    msgs[-1].wait_until_delivered()
-
-    ac2.start_io()
-
-    logging.info("wait for ac2 to receive a reaction")
-    msg2 = Message(ac2, ac2.wait_for_reactions_changed().msg_id)
-    assert msg2.get_sender_contact().get_snapshot().address == ac1_addr
-    assert msg2.get_snapshot().download_state == DownloadState.AVAILABLE
-    reactions = msg2.get_reactions()
-    contacts = [Contact(ac2, int(i)) for i in reactions.reactions_by_contact]
-    assert len(contacts) == 1
-    assert contacts[0].get_snapshot().address == ac1_addr
-    assert list(reactions.reactions_by_contact.values())[0] == [react_str]
-
-
-@pytest.mark.parametrize("n_accounts", [3, 2])
-def test_download_limit_chat_assignment(acfactory, tmp_path, n_accounts):
-    download_limit = 300000
-
-    alice, *others = acfactory.get_online_accounts(n_accounts)
-    bob = others[0]
-
-    alice_group = alice.create_group("test group")
-    for account in others:
-        chat = account.create_chat(alice)
-        chat.send_text("Hello Alice!")
-        assert alice.wait_for_incoming_msg().get_snapshot().text == "Hello Alice!"
-
-        contact = alice.create_contact(account)
-        alice_group.add_contact(contact)
-
-    bob.set_config("download_limit", str(download_limit))
-
-    alice_group.send_text("hi")
-    snapshot = bob.wait_for_incoming_msg().get_snapshot()
-    assert snapshot.text == "hi"
-    bob_group = snapshot.chat
-
-    path = tmp_path / "large"
-    path.write_bytes(os.urandom(download_limit + 1))
-
-    for i in range(10):
-        logging.info("Sending message %s", i)
-        alice_group.send_file(str(path))
-        snapshot = bob.wait_for_incoming_msg().get_snapshot()
-        assert snapshot.download_state == DownloadState.AVAILABLE
-        assert snapshot.chat == bob_group
-
-
 def test_markseen_contact_request(acfactory):
     """
     Test that seen status is synchronized for contact request messages

python/tests/test_1_online.py

@@ -1,7 +1,6 @@
 import os
 import queue
 import sys
-import base64
 from datetime import datetime, timezone
 
 import pytest
@@ -222,38 +221,6 @@ def test_webxdc_huge_update(acfactory, data, lp):
     assert update["payload"] == payload
 
 
-def test_webxdc_download_on_demand(acfactory, data, lp):
-    ac1, ac2 = acfactory.get_online_accounts(2)
-    acfactory.introduce_each_other([ac1, ac2])
-    chat = acfactory.get_accepted_chat(ac1, ac2)
-
-    msg1 = Message.new_empty(ac1, "webxdc")
-    msg1.set_text("message1")
-    msg1.set_file(data.get_path("webxdc/minimal.xdc"))
-    msg1 = chat.send_msg(msg1)
-    assert msg1.is_webxdc()
-    assert msg1.filename
-
-    msg2 = ac2._evtracker.wait_next_incoming_message()
-    assert msg2.is_webxdc()
-
-    lp.sec("ac2 sets download limit")
-    ac2.set_config("download_limit", "100")
-    assert msg1.send_status_update({"payload": base64.b64encode(os.urandom(300000))}, "some test data")
-    ac2_update = ac2._evtracker.wait_next_incoming_message()
-    assert ac2_update.download_state == dc.const.DC_DOWNLOAD_AVAILABLE
-    assert not msg2.get_status_updates()
-
-    ac2_update.download_full()
-    ac2._evtracker.get_matching("DC_EVENT_WEBXDC_STATUS_UPDATE")
-    assert msg2.get_status_updates()
-
-    # Get a event notifying that the message disappeared from the chat.
-    msgs_changed_event = ac2._evtracker.get_matching("DC_EVENT_MSGS_CHANGED")
-    assert msgs_changed_event.data1 == msg2.chat.id
-    assert msgs_changed_event.data2 == 0
-
-
 def test_enable_mvbox_move(acfactory, lp):
     (ac1,) = acfactory.get_online_accounts(1)
 

src/calls/calls_tests.rs

@@ -2,7 +2,7 @@ use super::*;
 use crate::chat::forward_msgs;
 use crate::config::Config;
 use crate::constants::DC_CHAT_ID_TRASH;
-use crate::receive_imf::{receive_imf, receive_imf_from_inbox};
+use crate::receive_imf::receive_imf;
 use crate::test_utils::{TestContext, TestContextManager};
 
 struct CallSetup {
@@ -610,65 +610,3 @@ async fn test_end_text_call() -> Result<()> {
 
     Ok(())
 }
-
-/// Tests that partially downloaded "call ended"
-/// messages are not processed.
-#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn test_no_partial_calls() -> Result<()> {
-    let mut tcm = TestContextManager::new();
-    let alice = &tcm.alice().await;
-
-    let seen = false;
-
-    // The messages in the test
-    // have no `Date` on purpose,
-    // so they are treated as new.
-    let received_call = receive_imf(
-        alice,
-        b"From: bob@example.net\n\
-        To: alice@example.org\n\
-        Message-ID: <first@example.net>\n\
-        Chat-Version: 1.0\n\
-        Chat-Content: call\n\
-        Chat-Webrtc-Room: YWFhYWFhYWFhCg==\n\
-        \n\
-        Hello, this is a call\n",
-        seen,
-    )
-    .await?
-    .unwrap();
-    assert_eq!(received_call.msg_ids.len(), 1);
-    let call_msg = Message::load_from_db(alice, received_call.msg_ids[0])
-        .await
-        .unwrap();
-    assert_eq!(call_msg.viewtype, Viewtype::Call);
-    assert_eq!(call_state(alice, call_msg.id).await?, CallState::Alerting);
-
-    let imf_raw = b"From: bob@example.net\n\
-        To: alice@example.org\n\
-        Message-ID: <second@example.net>\n\
-        In-Reply-To: <first@example.net>\n\
-        Chat-Version: 1.0\n\
-        Chat-Content: call-ended\n\
-        \n\
-        Call ended\n";
-    receive_imf_from_inbox(
-        alice,
-        "second@example.net",
-        imf_raw,
-        seen,
-        Some(imf_raw.len().try_into().unwrap()),
-    )
-    .await?;
-
-    // The call is still not ended.
-    assert_eq!(call_state(alice, call_msg.id).await?, CallState::Alerting);
-
-    // Fully downloading the message ends the call.
-    receive_imf_from_inbox(alice, "second@example.net", imf_raw, seen, None)
-        .await
-        .context("Failed to fully download end call message")?;
-    assert_eq!(call_state(alice, call_msg.id).await?, CallState::Missed);
-
-    Ok(())
-}

src/chat.rs

@@ -12,6 +12,7 @@ use std::time::Duration;
 use anyhow::{Context as _, Result, anyhow, bail, ensure};
 use chrono::TimeZone;
 use deltachat_contact_tools::{ContactAddress, sanitize_bidi_characters, sanitize_single_line};
+use humansize::{BINARY, format_size};
 use mail_builder::mime::MimePart;
 use serde::{Deserialize, Serialize};
 use strum_macros::EnumIter;
@@ -27,7 +28,9 @@ use crate::constants::{
 use crate::contact::{self, Contact, ContactId, Origin};
 use crate::context::Context;
 use crate::debug_logging::maybe_set_logging_xdc;
-use crate::download::DownloadState;
+use crate::download::{
+    DownloadState, PRE_MSG_ATTACHMENT_SIZE_THRESHOLD, PRE_MSG_SIZE_WARNING_THRESHOLD,
+};
 use crate::ephemeral::{Timer as EphemeralTimer, start_chat_ephemeral_timers};
 use crate::events::EventType;
 use crate::key::self_fingerprint;
@@ -35,7 +38,7 @@ use crate::location;
 use crate::log::{LogExt, warn};
 use crate::logged_debug_assert;
 use crate::message::{self, Message, MessageState, MsgId, Viewtype};
-use crate::mimefactory::MimeFactory;
+use crate::mimefactory::{MimeFactory, RenderedEmail};
 use crate::mimeparser::SystemMessage;
 use crate::param::{Param, Params};
 use crate::receive_imf::ReceivedMsg;
@@ -2728,6 +2731,57 @@ async fn prepare_send_msg(
     Ok(row_ids)
 }
 
+/// Renders the Message or splits it into Post-Message and Pre-Message.
+///
+/// Pre-Message is a small message with metadata which announces a larger Post-Message.
+/// Post-Messages are not downloaded in the background.
+///
+/// If pre-message is not nessesary this returns a normal message instead.
+async fn render_mime_message_and_pre_message(
+    context: &Context,
+    msg: &mut Message,
+    mimefactory: MimeFactory,
+) -> Result<(RenderedEmail, Option<RenderedEmail>)> {
+    let needs_pre_message = msg.viewtype.has_file()
+        && mimefactory.will_be_encrypted() // unencrypted is likely email, we don't want to spam by sending multiple messages
+        && msg
+            .get_filebytes(context)
+            .await?
+            .context("filebytes not available, even though message has attachment")?
+            > PRE_MSG_ATTACHMENT_SIZE_THRESHOLD;
+
+    if needs_pre_message {
+        info!(
+            context,
+            "Message is large and will be split into a pre- and a post-message.",
+        );
+
+        let mut mimefactory_post_msg = mimefactory.clone();
+        mimefactory_post_msg.set_as_post_message();
+        let rendered_msg = mimefactory_post_msg.render(context).await?;
+
+        let mut mimefactory_pre_msg = mimefactory;
+        mimefactory_pre_msg.set_as_pre_message_for(&rendered_msg);
+        let rendered_pre_msg = mimefactory_pre_msg
+            .render(context)
+            .await
+            .context("pre-message failed to render")?;
+
+        if rendered_pre_msg.message.len() > PRE_MSG_SIZE_WARNING_THRESHOLD {
+            warn!(
+                context,
+                "Pre-message for message (MsgId={}) is larger than expected: {}.",
+                msg.id,
+                rendered_pre_msg.message.len()
+            );
+        }
+
+        Ok((rendered_msg, Some(rendered_pre_msg)))
+    } else {
+        Ok((mimefactory.render(context).await?, None))
+    }
+}
+
 /// Constructs jobs for sending a message and inserts them into the appropriate table.
 ///
 /// Updates the message `GuaranteeE2ee` parameter and persists it
@@ -2799,13 +2853,29 @@ pub(crate) async fn create_send_msg_jobs(context: &Context, msg: &mut Message) -
         return Ok(Vec::new());
     }
 
-    let rendered_msg = match mimefactory.render(context).await {
-        Ok(res) => Ok(res),
-        Err(err) => {
-            message::set_msg_failed(context, msg, &err.to_string()).await?;
-            Err(err)
-        }
-    }?;
+    let (rendered_msg, rendered_pre_msg) =
+        match render_mime_message_and_pre_message(context, msg, mimefactory).await {
+            Ok(res) => Ok(res),
+            Err(err) => {
+                message::set_msg_failed(context, msg, &err.to_string()).await?;
+                Err(err)
+            }
+        }?;
+
+    if let (post_msg, Some(pre_msg)) = (&rendered_msg, &rendered_pre_msg) {
+        info!(
+            context,
+            "Message Sizes: Pre-Message {}; Post-Message: {}",
+            format_size(pre_msg.message.len(), BINARY),
+            format_size(post_msg.message.len(), BINARY)
+        );
+    } else {
+        info!(
+            context,
+            "Message will be sent as normal message (no pre- and post message). Size: {}",
+            format_size(rendered_msg.message.len(), BINARY)
+        );
+    }
 
     if needs_encryption && !rendered_msg.is_encrypted {
         /* unrecoverable */
@@ -2864,12 +2934,26 @@ pub(crate) async fn create_send_msg_jobs(context: &Context, msg: &mut Message) -
         } else {
             for recipients_chunk in recipients.chunks(chunk_size) {
                 let recipients_chunk = recipients_chunk.join(" ");
+                // send pre-message before actual message
+                if let Some(pre_msg) = &rendered_pre_msg {
+                    let row_id = t.execute(
+                        "INSERT INTO smtp (rfc724_mid, recipients, mime, msg_id)
+                        VALUES            (?1,         ?2,         ?3,   ?4)",
+                        (
+                            &pre_msg.rfc724_mid,
+                            &recipients_chunk,
+                            &pre_msg.message,
+                            msg.id,
+                        ),
+                    )?;
+                    row_ids.push(row_id.try_into()?);
+                }
                 let row_id = t.execute(
-                    "INSERT INTO smtp (rfc724_mid, recipients, mime, msg_id) \
+                    "INSERT INTO smtp (rfc724_mid, recipients, mime, msg_id)
                     VALUES            (?1,         ?2,         ?3,   ?4)",
                     (
                         &rendered_msg.rfc724_mid,
-                        recipients_chunk,
+                        &recipients_chunk,
                         &rendered_msg.message,
                         msg.id,
                     ),
@@ -4256,6 +4340,14 @@ pub async fn forward_msgs_2ctx(
             msg.viewtype = Viewtype::Text;
         }
 
+        if msg.download_state != DownloadState::Done {
+            // we don't use Message.get_text() here,
+            // because it may change in future,
+            // when UI shows this info itself,
+            // then the additional_text will not be added in get_text anymore.
+            msg.text += &msg.additional_text;
+        }
+
         let param = &mut param;
         msg.param.steal(param, Param::File);
         msg.param.steal(param, Param::Filename);
@@ -4266,6 +4358,7 @@ pub async fn forward_msgs_2ctx(
         msg.param.steal(param, Param::ProtectQuote);
         msg.param.steal(param, Param::Quote);
         msg.param.steal(param, Param::Summary1);
+
         msg.in_reply_to = None;
 
         // do not leak data as group names; a default subject is generated by mimefactory
@@ -4332,12 +4425,22 @@ pub(crate) async fn save_copy_in_self_talk(
     msg.param.remove(Param::WebxdcDocumentTimestamp);
     msg.param.remove(Param::WebxdcSummary);
     msg.param.remove(Param::WebxdcSummaryTimestamp);
+    msg.param.remove(Param::PostMessageFileBytes);
+    msg.param.remove(Param::PostMessageViewtype);
+
+    if msg.download_state != DownloadState::Done {
+        // we don't use Message.get_text() here,
+        // because it may change in future,
+        // when UI shows this info itself,
+        // then the additional_text will not be added in get_text anymore.
+        msg.text += &msg.additional_text;
+    }
 
     if !msg.original_msg_id.is_unset() {
         bail!("message already saved.");
     }
 
-    let copy_fields = "from_id, to_id, timestamp_rcvd, type, txt,
+    let copy_fields = "from_id, to_id, timestamp_rcvd, type,
                        mime_modified, mime_headers, mime_compressed, mime_in_reply_to, subject, msgrmsg";
     let row_id = context
         .sql
@@ -4345,7 +4448,7 @@ pub(crate) async fn save_copy_in_self_talk(
             &format!(
                 "INSERT INTO msgs ({copy_fields},
                                    timestamp_sent,
-                                   chat_id, rfc724_mid, state, timestamp, param, starred)
+                                   txt, chat_id, rfc724_mid, state, timestamp, param, starred)
                  SELECT            {copy_fields},
                                    -- Outgoing messages on originating device
                                    -- have timestamp_sent == 0.
@@ -4353,10 +4456,11 @@ pub(crate) async fn save_copy_in_self_talk(
                                    -- so UIs display the same timestamp
                                    -- for saved and original message.
                                    IIF(timestamp_sent == 0, timestamp, timestamp_sent),
-                                   ?, ?, ?, ?, ?, ?
+                                   ?, ?, ?, ?, ?, ?, ?
                  FROM msgs WHERE id=?;"
             ),
             (
+                msg.text,
                 dest_chat_id,
                 dest_rfc724_mid,
                 if msg.from_id == ContactId::SELF {

src/chat/chat_tests.rs

@@ -3116,7 +3116,7 @@ async fn test_broadcast_channel_protected_listid() -> Result<()> {
         .await?
         .grpid;
 
-    let parsed = mimeparser::MimeMessage::from_bytes(bob, sent.payload.as_bytes(), None).await?;
+    let parsed = mimeparser::MimeMessage::from_bytes(bob, sent.payload.as_bytes()).await?;
     assert_eq!(
         parsed.get_mailinglist_header().unwrap(),
         format!("My Channel <{}>", alice_list_id)
@@ -3311,7 +3311,7 @@ async fn test_leave_broadcast_multidevice() -> Result<()> {
     remove_contact_from_chat(bob0, bob_chat_id, ContactId::SELF).await?;
 
     let leave_msg = bob0.pop_sent_msg().await;
-    let parsed = MimeMessage::from_bytes(bob1, leave_msg.payload().as_bytes(), None).await?;
+    let parsed = MimeMessage::from_bytes(bob1, leave_msg.payload().as_bytes()).await?;
     assert_eq!(parsed.parts[0].msg, "I left the group.");
 
     let rcvd = bob1.recv_msg(&leave_msg).await;

src/config.rs

@@ -438,14 +438,20 @@ pub enum Config {
     /// using this still run unmodified code.
     TestHooks,
 
-    /// Return an error from `receive_imf_inner()` for a fully downloaded message. For tests.
-    FailOnReceivingFullMsg,
-
     /// Enable composing emails with Header Protection as defined in
     /// <https://www.rfc-editor.org/rfc/rfc9788.html> "Header Protection for Cryptographically
     /// Protected Email".
     #[strum(props(default = "1"))]
     StdHeaderProtectionComposing,
+
+    /// Return an error from `receive_imf_inner()`. For tests.
+    SimulateReceiveImfError,
+
+    /// Disable the addition of the metadata to the text field of Pre-Messages.
+    ///
+    /// This is used by tests and can be used in the UI,
+    /// when the UI wants to displays that information in a prettier manner.
+    HidePreMessageMetadataText,
 }
 
 impl Config {

src/context.rs

@@ -609,7 +609,7 @@ impl Context {
                     convert_folder_meaning(self, folder_meaning).await?
                 {
                     connection
-                        .fetch_move_delete(self, &mut session, &watch_folder, folder_meaning)
+                        .fetch_move_delete(self, &mut session, true, &watch_folder, folder_meaning)
                         .await?;
                 }
             }
@@ -622,6 +622,12 @@ impl Context {
             {
                 warn!(self, "Failed to update quota: {err:#}.");
             }
+
+            // OPTIONAL TODO: if time left start downloading messages
+            // while (msg = download_when_normal_starts) {
+            //  if not time_left {break;}
+            //  connection.download_message(msg) }
+            // }
         }
 
         info!(
@@ -1081,16 +1087,16 @@ impl Context {
                 .unwrap_or_default(),
         );
         res.insert(
-            "fail_on_receiving_full_msg",
+            "std_header_protection_composing",
             self.sql
-                .get_raw_config("fail_on_receiving_full_msg")
+                .get_raw_config("std_header_protection_composing")
                 .await?
                 .unwrap_or_default(),
         );
         res.insert(
-            "std_header_protection_composing",
+            "hide_pre_message_metadata_text",
             self.sql
-                .get_raw_config("std_header_protection_composing")
+                .get_raw_config("hide_pre_message_metadata_text")
                 .await?
                 .unwrap_or_default(),
         );

src/context/context_tests.rs

@@ -297,6 +297,7 @@ async fn test_get_info_completeness() {
         "encrypted_device_token",
         "stats_last_update",
         "stats_last_old_contact_id",
+        "simulate_receive_imf_error", // only used in tests
     ];
     let t = TestContext::new().await;
     let info = t.get_info().await.unwrap();

src/download.rs

@@ -1,27 +1,18 @@
 //! # Download large messages manually.
 
-use std::cmp::max;
 use std::collections::BTreeMap;
 
 use anyhow::{Result, anyhow, bail, ensure};
 use deltachat_derive::{FromSql, ToSql};
 use serde::{Deserialize, Serialize};
 
-use crate::config::Config;
 use crate::context::Context;
 use crate::imap::session::Session;
-use crate::message::{Message, MsgId, Viewtype};
-use crate::mimeparser::{MimeMessage, Part};
-use crate::tools::time;
-use crate::{EventType, chatlist_events, stock_str};
+use crate::log::warn;
+use crate::message::{self, Message, MsgId, rfc724_mid_exists};
+use crate::{EventType, chatlist_events};
 
-/// Download limits should not be used below `MIN_DOWNLOAD_LIMIT`.
-///
-/// For better UX, some messages as add-member, non-delivery-reports (NDN) or read-receipts (MDN)
-/// should always be downloaded completely to handle them correctly,
-/// also in larger groups and if group and contact avatar are attached.
-/// Most of these cases are caught by `MIN_DOWNLOAD_LIMIT`.
-pub(crate) const MIN_DOWNLOAD_LIMIT: u32 = 163840;
+pub(crate) mod pre_msg_metadata;
 
 /// If a message is downloaded only partially
 /// and `delete_server_after` is set to small timeouts (eg. "at once"),
@@ -29,6 +20,21 @@ pub(crate) const MIN_DOWNLOAD_LIMIT: u32 = 163840;
 /// `MIN_DELETE_SERVER_AFTER` increases the timeout in this case.
 pub(crate) const MIN_DELETE_SERVER_AFTER: i64 = 48 * 60 * 60;
 
+/// From this point onward outgoing messages are considered large
+/// and get a Pre-Message, which announces the Post-Message.
+// this is only about sending so we can modify it any time.
+// current value is a bit less than the minimum auto download setting from the UIs (which is 160 KiB)
+pub(crate) const PRE_MSG_ATTACHMENT_SIZE_THRESHOLD: u64 = 140_000;
+
+/// Max message size to be fetched in the background.
+/// This limit defines what messages are fully fetched in the background.
+/// This is for all messages that don't have the Post-Message header.
+pub(crate) const MAX_FETCH_MSG_SIZE: u32 = 1_000_000;
+
+/// Max size for pre messages. A warning is emitted when this is exceeded.
+/// Should be well below `MAX_FETCH_MSG_SIZE`
+pub(crate) const PRE_MSG_SIZE_WARNING_THRESHOLD: usize = 150_000;
+
 /// Download state of the message.
 #[derive(
     Debug,
@@ -64,20 +70,8 @@ pub enum DownloadState {
     InProgress = 1000,
 }
 
-impl Context {
-    // Returns validated download limit or `None` for "no limit".
-    pub(crate) async fn download_limit(&self) -> Result<Option<u32>> {
-        let download_limit = self.get_config_int(Config::DownloadLimit).await?;
-        if download_limit <= 0 {
-            Ok(None)
-        } else {
-            Ok(Some(max(MIN_DOWNLOAD_LIMIT, download_limit as u32)))
-        }
-    }
-}
-
 impl MsgId {
-    /// Schedules full message download for partially downloaded message.
+    /// Schedules Post-Message download for partially downloaded message.
     pub async fn download_full(self, context: &Context) -> Result<()> {
         let msg = Message::load_from_db(context, self).await?;
         match msg.download_state() {
@@ -86,11 +80,17 @@ impl MsgId {
             }
             DownloadState::InProgress => return Err(anyhow!("Download already in progress.")),
             DownloadState::Available | DownloadState::Failure => {
+                if msg.rfc724_mid().is_empty() {
+                    return Err(anyhow!("Download not possible, message has no rfc724_mid"));
+                }
                 self.update_download_state(context, DownloadState::InProgress)
                     .await?;
                 context
                     .sql
-                    .execute("INSERT INTO download (msg_id) VALUES (?)", (self,))
+                    .execute(
+                        "INSERT INTO download (rfc724_mid) VALUES (?)",
+                        (msg.rfc724_mid(),),
+                    )
                     .await?;
                 context.scheduler.interrupt_inbox().await;
             }
@@ -139,25 +139,14 @@ impl Message {
 /// Most messages are downloaded automatically on fetch instead.
 pub(crate) async fn download_msg(
     context: &Context,
-    msg_id: MsgId,
+    rfc724_mid: String,
     session: &mut Session,
 ) -> Result<()> {
-    let Some(msg) = Message::load_from_db_optional(context, msg_id).await? else {
-        // If partially downloaded message was already deleted
-        // we do not know its Message-ID anymore
-        // so cannot download it.
-        //
-        // Probably the message expired due to `delete_device_after`
-        // setting or was otherwise removed from the device,
-        // so we don't want it to reappear anyway.
-        return Ok(());
-    };
-
     let row = context
         .sql
         .query_row_optional(
             "SELECT uid, folder FROM imap WHERE rfc724_mid=? AND target!=''",
-            (&msg.rfc724_mid,),
+            (&rfc724_mid,),
             |row| {
                 let server_uid: u32 = row.get(0)?;
                 let server_folder: String = row.get(1)?;
@@ -172,7 +161,7 @@ pub(crate) async fn download_msg(
     };
 
     session
-        .fetch_single_msg(context, &server_folder, server_uid, msg.rfc724_mid.clone())
+        .fetch_single_msg(context, &server_folder, server_uid, rfc724_mid)
         .await?;
     Ok(())
 }
@@ -205,7 +194,7 @@ impl Session {
         let mut uid_message_ids: BTreeMap<u32, String> = BTreeMap::new();
         uid_message_ids.insert(uid, rfc724_mid);
         let (sender, receiver) = async_channel::unbounded();
-        self.fetch_many_msgs(context, folder, vec![uid], &uid_message_ids, false, sender)
+        self.fetch_many_msgs(context, folder, vec![uid], &uid_message_ids, sender)
             .await?;
         if receiver.recv().await.is_err() {
             bail!("Failed to fetch UID {uid}");
@@ -214,41 +203,143 @@ impl Session {
     }
 }
 
-impl MimeMessage {
-    /// Creates a placeholder part and add that to `parts`.
-    ///
-    /// To create the placeholder, only the outermost header can be used,
-    /// the mime-structure itself is not available.
-    ///
-    /// The placeholder part currently contains a text with size and availability of the message.
-    pub(crate) async fn create_stub_from_partial_download(
-        &mut self,
-        context: &Context,
-        org_bytes: u32,
-    ) -> Result<()> {
-        let mut text = format!(
-            "[{}]",
-            stock_str::partial_download_msg_body(context, org_bytes).await
-        );
-        if let Some(delete_server_after) = context.get_config_delete_server_after().await? {
-            let until = stock_str::download_availability(
-                context,
-                time() + max(delete_server_after, MIN_DELETE_SERVER_AFTER),
-            )
-            .await;
-            text += format!(" [{until}]").as_str();
-        };
-
-        info!(context, "Partial download: {}", text);
-
-        self.do_add_single_part(Part {
-            typ: Viewtype::Text,
-            msg: text,
-            ..Default::default()
-        });
-
-        Ok(())
+async fn set_msg_state_to_failed(context: &Context, rfc724_mid: &str) -> Result<()> {
+    if let Some(msg_id) = rfc724_mid_exists(context, rfc724_mid).await? {
+        // Update download state to failure
+        // so it can be retried.
+        //
+        // On success update_download_state() is not needed
+        // as receive_imf() already
+        // set the state and emitted the event.
+        msg_id
+            .update_download_state(context, DownloadState::Failure)
+            .await?;
     }
+    Ok(())
+}
+
+async fn available_post_msgs_contains_rfc724_mid(
+    context: &Context,
+    rfc724_mid: &str,
+) -> Result<bool> {
+    Ok(context
+        .sql
+        .query_get_value::<String>(
+            "SELECT rfc724_mid FROM available_post_msgs WHERE rfc724_mid=?",
+            (&rfc724_mid,),
+        )
+        .await?
+        .is_some())
+}
+
+async fn remove_from_available_post_msgs_table(context: &Context, rfc724_mid: &str) -> Result<()> {
+    context
+        .sql
+        .execute(
+            "DELETE FROM available_post_msgs WHERE rfc724_mid=?",
+            (&rfc724_mid,),
+        )
+        .await?;
+    Ok(())
+}
+
+async fn remove_from_download_table(context: &Context, rfc724_mid: &str) -> Result<()> {
+    context
+        .sql
+        .execute("DELETE FROM download WHERE rfc724_mid=?", (&rfc724_mid,))
+        .await?;
+    Ok(())
+}
+
+// this is a dedicated method because it is used in multiple places.
+pub(crate) async fn premessage_is_downloaded_for(
+    context: &Context,
+    rfc724_mid: &str,
+) -> Result<bool> {
+    Ok(message::rfc724_mid_exists(context, rfc724_mid)
+        .await?
+        .is_some())
+}
+
+pub(crate) async fn download_msgs(context: &Context, session: &mut Session) -> Result<()> {
+    let rfc724_mids = context
+        .sql
+        .query_map_vec("SELECT rfc724_mid FROM download", (), |row| {
+            let rfc724_mid: String = row.get(0)?;
+            Ok(rfc724_mid)
+        })
+        .await?;
+
+    for rfc724_mid in &rfc724_mids {
+        let res = download_msg(context, rfc724_mid.clone(), session).await;
+        if res.is_ok() {
+            remove_from_download_table(context, rfc724_mid).await?;
+            remove_from_available_post_msgs_table(context, rfc724_mid).await?;
+        }
+        if let Err(err) = res {
+            warn!(
+                context,
+                "Failed to download message rfc724_mid={rfc724_mid}: {:#}.", err
+            );
+            if !premessage_is_downloaded_for(context, rfc724_mid).await? {
+                // This is probably a classical email that vanished before we could download it
+                warn!(
+                    context,
+                    "{rfc724_mid} is probably a classical email that vanished before we could download it"
+                );
+                remove_from_download_table(context, rfc724_mid).await?;
+            } else if available_post_msgs_contains_rfc724_mid(context, rfc724_mid).await? {
+                warn!(
+                    context,
+                    "{rfc724_mid} is in available_post_msgs table but we failed to fetch it,
+                    so set the message to DownloadState::Failure - probably it was deleted on the server in the meantime"
+                );
+                set_msg_state_to_failed(context, rfc724_mid).await?;
+                remove_from_download_table(context, rfc724_mid).await?;
+                remove_from_available_post_msgs_table(context, rfc724_mid).await?;
+            } else {
+                // leave the message in DownloadState::InProgress;
+                // it will be downloaded once it arrives.
+            }
+        }
+    }
+
+    Ok(())
+}
+
+/// Download known post messages without pre_message
+/// in order to guard against lost pre-messages:
+pub(crate) async fn download_known_post_messages_without_pre_message(
+    context: &Context,
+    session: &mut Session,
+) -> Result<()> {
+    let rfc724_mids = context
+        .sql
+        .query_map_vec("SELECT rfc724_mid FROM available_post_msgs", (), |row| {
+            let rfc724_mid: String = row.get(0)?;
+            Ok(rfc724_mid)
+        })
+        .await?;
+    for rfc724_mid in &rfc724_mids {
+        if !premessage_is_downloaded_for(context, rfc724_mid).await? {
+            // Download the Post-Message unconditionally,
+            // because the Pre-Message got lost.
+            // The message may be in the wrong order,
+            // but at least we have it at all.
+            let res = download_msg(context, rfc724_mid.clone(), session).await;
+            if res.is_ok() {
+                remove_from_available_post_msgs_table(context, rfc724_mid).await?;
+            }
+            if let Err(err) = res {
+                warn!(
+                    context,
+                    "download_known_post_messages_without_pre_message: Failed to download message rfc724_mid={rfc724_mid}: {:#}.",
+                    err
+                );
+            }
+        }
+    }
+    Ok(())
 }
 
 #[cfg(test)]
@@ -256,11 +347,8 @@ mod tests {
     use num_traits::FromPrimitive;
 
     use super::*;
-    use crate::chat::{get_chat_msgs, send_msg};
-    use crate::ephemeral::Timer;
-    use crate::message::delete_msgs;
-    use crate::receive_imf::receive_imf_from_inbox;
-    use crate::test_utils::{E2EE_INFO_MSGS, TestContext, TestContextManager};
+    use crate::chat::send_msg;
+    use crate::test_utils::TestContext;
 
     #[test]
     fn test_downloadstate_values() {
@@ -278,29 +366,6 @@ mod tests {
         );
     }
 
-    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-    async fn test_download_limit() -> Result<()> {
-        let t = TestContext::new_alice().await;
-
-        assert_eq!(t.download_limit().await?, None);
-
-        t.set_config(Config::DownloadLimit, Some("200000")).await?;
-        assert_eq!(t.download_limit().await?, Some(200000));
-
-        t.set_config(Config::DownloadLimit, Some("20000")).await?;
-        assert_eq!(t.download_limit().await?, Some(MIN_DOWNLOAD_LIMIT));
-
-        t.set_config(Config::DownloadLimit, None).await?;
-        assert_eq!(t.download_limit().await?, None);
-
-        for val in &["0", "-1", "-100", "", "foo"] {
-            t.set_config(Config::DownloadLimit, Some(val)).await?;
-            assert_eq!(t.download_limit().await?, None);
-        }
-
-        Ok(())
-    }
-
     #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
     async fn test_update_download_state() -> Result<()> {
         let t = TestContext::new_alice().await;
@@ -333,229 +398,5 @@ mod tests {
         Ok(())
     }
 
-    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-    async fn test_partial_receive_imf() -> Result<()> {
-        let t = TestContext::new_alice().await;
-
-        let header = "Received: (Postfix, from userid 1000); Mon, 4 Dec 2006 14:51:39 +0100 (CET)\n\
-             From: bob@example.com\n\
-             To: alice@example.org\n\
-             Subject: foo\n\
-             Message-ID: <Mr.12345678901@example.com>\n\
-             Chat-Version: 1.0\n\
-             Date: Sun, 22 Mar 2020 22:37:57 +0000\
-             Content-Type: text/plain";
-
-        receive_imf_from_inbox(
-            &t,
-            "Mr.12345678901@example.com",
-            header.as_bytes(),
-            false,
-            Some(100000),
-        )
-        .await?;
-        let msg = t.get_last_msg().await;
-        assert_eq!(msg.download_state(), DownloadState::Available);
-        assert_eq!(msg.get_subject(), "foo");
-        assert!(
-            msg.get_text()
-                .contains(&stock_str::partial_download_msg_body(&t, 100000).await)
-        );
-
-        receive_imf_from_inbox(
-            &t,
-            "Mr.12345678901@example.com",
-            format!("{header}\n\n100k text...").as_bytes(),
-            false,
-            None,
-        )
-        .await?;
-        let msg = t.get_last_msg().await;
-        assert_eq!(msg.download_state(), DownloadState::Done);
-        assert_eq!(msg.get_subject(), "foo");
-        assert_eq!(msg.get_text(), "100k text...");
-
-        Ok(())
-    }
-
-    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-    async fn test_partial_download_and_ephemeral() -> Result<()> {
-        let t = TestContext::new_alice().await;
-        let chat_id = t
-            .create_chat_with_contact("bob", "bob@example.org")
-            .await
-            .id;
-        chat_id
-            .set_ephemeral_timer(&t, Timer::Enabled { duration: 60 })
-            .await?;
-
-        // download message from bob partially, this must not change the ephemeral timer
-        receive_imf_from_inbox(
-            &t,
-            "first@example.org",
-            b"From: Bob <bob@example.org>\n\
-                    To: Alice <alice@example.org>\n\
-                    Chat-Version: 1.0\n\
-                    Subject: subject\n\
-                    Message-ID: <first@example.org>\n\
-                    Date: Sun, 14 Nov 2021 00:10:00 +0000\
-                    Content-Type: text/plain",
-            false,
-            Some(100000),
-        )
-        .await?;
-        assert_eq!(
-            chat_id.get_ephemeral_timer(&t).await?,
-            Timer::Enabled { duration: 60 }
-        );
-
-        Ok(())
-    }
-
-    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-    async fn test_status_update_expands_to_nothing() -> Result<()> {
-        let alice = TestContext::new_alice().await;
-        let bob = TestContext::new_bob().await;
-        let chat_id = alice.create_chat(&bob).await.id;
-
-        let file = alice.get_blobdir().join("minimal.xdc");
-        tokio::fs::write(&file, include_bytes!("../test-data/webxdc/minimal.xdc")).await?;
-        let mut instance = Message::new(Viewtype::File);
-        instance.set_file_and_deduplicate(&alice, &file, None, None)?;
-        let _sent1 = alice.send_msg(chat_id, &mut instance).await;
-
-        alice
-            .send_webxdc_status_update(instance.id, r#"{"payload":7}"#)
-            .await?;
-        alice.flush_status_updates().await?;
-        let sent2 = alice.pop_sent_msg().await;
-        let sent2_rfc724_mid = sent2.load_from_db().await.rfc724_mid;
-
-        // not downloading the status update results in an placeholder
-        receive_imf_from_inbox(
-            &bob,
-            &sent2_rfc724_mid,
-            sent2.payload().as_bytes(),
-            false,
-            Some(sent2.payload().len() as u32),
-        )
-        .await?;
-        let msg = bob.get_last_msg().await;
-        let chat_id = msg.chat_id;
-        assert_eq!(
-            get_chat_msgs(&bob, chat_id).await?.len(),
-            E2EE_INFO_MSGS + 1
-        );
-        assert_eq!(msg.download_state(), DownloadState::Available);
-
-        // downloading the status update afterwards expands to nothing and moves the placeholder to trash-chat
-        // (usually status updates are too small for not being downloaded directly)
-        receive_imf_from_inbox(
-            &bob,
-            &sent2_rfc724_mid,
-            sent2.payload().as_bytes(),
-            false,
-            None,
-        )
-        .await?;
-        assert_eq!(get_chat_msgs(&bob, chat_id).await?.len(), E2EE_INFO_MSGS);
-        assert!(
-            Message::load_from_db_optional(&bob, msg.id)
-                .await?
-                .is_none()
-        );
-
-        Ok(())
-    }
-
-    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-    async fn test_mdn_expands_to_nothing() -> Result<()> {
-        let bob = TestContext::new_bob().await;
-        let raw = b"Subject: Message opened\n\
-            Date: Mon, 10 Jan 2020 00:00:00 +0000\n\
-            Chat-Version: 1.0\n\
-            Message-ID: <bar@example.org>\n\
-            To: Alice <alice@example.org>\n\
-            From: Bob <bob@example.org>\n\
-            Content-Type: multipart/report; report-type=disposition-notification;\n\t\
-            boundary=\"kJBbU58X1xeWNHgBtTbMk80M5qnV4N\"\n\
-            \n\
-            \n\
-            --kJBbU58X1xeWNHgBtTbMk80M5qnV4N\n\
-            Content-Type: text/plain; charset=utf-8\n\
-            \n\
-            bla\n\
-            \n\
-            \n\
-            --kJBbU58X1xeWNHgBtTbMk80M5qnV4N\n\
-            Content-Type: message/disposition-notification\n\
-            \n\
-            Reporting-UA: Delta Chat 1.88.0\n\
-            Original-Recipient: rfc822;bob@example.org\n\
-            Final-Recipient: rfc822;bob@example.org\n\
-            Original-Message-ID: <foo@example.org>\n\
-            Disposition: manual-action/MDN-sent-automatically; displayed\n\
-            \n\
-            \n\
-            --kJBbU58X1xeWNHgBtTbMk80M5qnV4N--\n\
-            ";
-
-        // not downloading the mdn results in an placeholder
-        receive_imf_from_inbox(&bob, "bar@example.org", raw, false, Some(raw.len() as u32)).await?;
-        let msg = bob.get_last_msg().await;
-        let chat_id = msg.chat_id;
-        assert_eq!(get_chat_msgs(&bob, chat_id).await?.len(), 1);
-        assert_eq!(msg.download_state(), DownloadState::Available);
-
-        // downloading the mdn afterwards expands to nothing and deletes the placeholder directly
-        // (usually mdn are too small for not being downloaded directly)
-        receive_imf_from_inbox(&bob, "bar@example.org", raw, false, None).await?;
-        assert_eq!(get_chat_msgs(&bob, chat_id).await?.len(), 0);
-        assert!(
-            Message::load_from_db_optional(&bob, msg.id)
-                .await?
-                .is_none()
-        );
-
-        Ok(())
-    }
-
-    /// Tests that fully downloading the message
-    /// works even if the Message-ID already exists
-    /// in the database assigned to the trash chat.
-    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-    async fn test_partial_download_trashed() -> Result<()> {
-        let mut tcm = TestContextManager::new();
-        let alice = &tcm.alice().await;
-
-        let imf_raw = b"From: Bob <bob@example.org>\n\
-              To: Alice <alice@example.org>\n\
-              Chat-Version: 1.0\n\
-              Subject: subject\n\
-              Message-ID: <first@example.org>\n\
-              Date: Sun, 14 Nov 2021 00:10:00 +0000\
-              Content-Type: text/plain";
-
-        // Download message from Bob partially.
-        let partial_received_msg =
-            receive_imf_from_inbox(alice, "first@example.org", imf_raw, false, Some(100000))
-                .await?
-                .unwrap();
-        assert_eq!(partial_received_msg.msg_ids.len(), 1);
-
-        // Delete the received message.
-        // Not it is still in the database,
-        // but in the trash chat.
-        delete_msgs(alice, &[partial_received_msg.msg_ids[0]]).await?;
-
-        // Fully download message after deletion.
-        let full_received_msg =
-            receive_imf_from_inbox(alice, "first@example.org", imf_raw, false, None).await?;
-
-        // The message does not reappear.
-        // However, `receive_imf` should not fail.
-        assert!(full_received_msg.is_none());
-
-        Ok(())
-    }
+    // NOTE: The download tests for pre-messages are in src/tests/pre_messages.rs
 }

src/download/pre_msg_metadata.rs

@@ -0,0 +1,248 @@
+use anyhow::{Context as _, Result};
+use num_traits::ToPrimitive;
+use serde::{Deserialize, Serialize};
+
+use crate::context::Context;
+use crate::log::warn;
+use crate::message::Message;
+use crate::message::Viewtype;
+use crate::param::{Param, Params};
+
+/// Metadata contained in Pre-Message that describes the Post-Message.
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub struct PreMsgMetadata {
+    /// size of the attachment in bytes
+    pub(crate) size: u64,
+    /// Real viewtype of message
+    pub(crate) viewtype: Viewtype,
+    /// the original file name
+    pub(crate) filename: String,
+    /// Dimensions: width and height of image or video
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub(crate) dimensions: Option<(i32, i32)>,
+    /// Duration of audio file or video in milliseconds
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub(crate) duration: Option<i32>,
+}
+
+impl PreMsgMetadata {
+    // Returns PreMsgMetadata for messages with files and None for messages without file attachment
+    pub(crate) async fn from_msg(context: &Context, message: &Message) -> Result<Option<Self>> {
+        if !message.viewtype.has_file() {
+            return Ok(None);
+        }
+
+        let size = message
+            .get_filebytes(context)
+            .await?
+            .context("unexpected: file has no size")?;
+        let filename = message
+            .param
+            .get(Param::Filename)
+            .unwrap_or_default()
+            .to_owned();
+        let dimensions = {
+            match (
+                message.param.get_int(Param::Width),
+                message.param.get_int(Param::Height),
+            ) {
+                (None, None) => None,
+                (Some(width), Some(height)) => Some((width, height)),
+                _ => {
+                    warn!(context, "Message has misses either width or height");
+                    None
+                }
+            }
+        };
+        let duration = message.param.get_int(Param::Duration);
+
+        Ok(Some(Self {
+            size,
+            filename,
+            viewtype: message.viewtype,
+            dimensions,
+            duration,
+        }))
+    }
+
+    pub(crate) fn to_header_value(&self) -> Result<String> {
+        Ok(serde_json::to_string(&self)?)
+    }
+
+    pub(crate) fn try_from_header_value(value: &str) -> Result<Self> {
+        Ok(serde_json::from_str(value)?)
+    }
+}
+
+impl Params {
+    /// Applies data from pre_msg_metadata to Params
+    pub(crate) fn apply_from_pre_msg_metadata(
+        &mut self,
+        pre_msg_metadata: &PreMsgMetadata,
+    ) -> &mut Self {
+        self.set(Param::PostMessageFileBytes, pre_msg_metadata.size);
+        if !pre_msg_metadata.filename.is_empty() {
+            self.set(Param::Filename, &pre_msg_metadata.filename);
+        }
+        self.set_i64(
+            Param::PostMessageViewtype,
+            pre_msg_metadata.viewtype.to_i64().unwrap_or_default(),
+        );
+        if let Some((width, height)) = pre_msg_metadata.dimensions {
+            self.set(Param::Width, width);
+            self.set(Param::Height, height);
+        }
+        if let Some(duration) = pre_msg_metadata.duration {
+            self.set(Param::Duration, duration);
+        }
+
+        self
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use anyhow::Result;
+    use pretty_assertions::assert_eq;
+
+    use crate::{
+        message::{Message, Viewtype},
+        test_utils::{TestContextManager, create_test_image},
+    };
+
+    use super::PreMsgMetadata;
+
+    /// Build from message with file attachment
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_build_from_file_msg() -> Result<()> {
+        let mut tcm = TestContextManager::new();
+        let alice = &tcm.alice().await;
+
+        let mut file_msg = Message::new(Viewtype::File);
+        file_msg.set_file_from_bytes(alice, "test.bin", &vec![0u8; 1_000_000], None)?;
+        let pre_mesage_metadata = PreMsgMetadata::from_msg(alice, &file_msg).await?;
+        assert_eq!(
+            pre_mesage_metadata,
+            Some(PreMsgMetadata {
+                size: 1_000_000,
+                viewtype: Viewtype::File,
+                filename: "test.bin".to_string(),
+                dimensions: None,
+                duration: None,
+            })
+        );
+        Ok(())
+    }
+
+    /// Build from message with image attachment
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_build_from_image_msg() -> Result<()> {
+        let mut tcm = TestContextManager::new();
+        let alice = &tcm.alice().await;
+        let mut image_msg = Message::new(Viewtype::Image);
+
+        let (width, height) = (1080, 1920);
+        let test_img = create_test_image(width, height)?;
+        image_msg.set_file_from_bytes(alice, "vacation.png", &test_img, None)?;
+        // this is usually done while sending,
+        // but we don't send it here, so we need to call it ourself
+        image_msg.try_calc_and_set_dimensions(alice).await?;
+        let pre_mesage_metadata = PreMsgMetadata::from_msg(alice, &image_msg).await?;
+        assert_eq!(
+            pre_mesage_metadata,
+            Some(PreMsgMetadata {
+                size: 1816098,
+                viewtype: Viewtype::Image,
+                filename: "vacation.png".to_string(),
+                dimensions: Some((width as i32, height as i32)),
+                duration: None,
+            })
+        );
+
+        Ok(())
+    }
+
+    /// Test that serialisation results in expected format
+    #[test]
+    fn test_serialize_to_header() -> Result<()> {
+        assert_eq!(
+            PreMsgMetadata {
+                size: 1_000_000,
+                viewtype: Viewtype::File,
+                filename: "test.bin".to_string(),
+                dimensions: None,
+                duration: None,
+            }
+            .to_header_value()?,
+            "{\"size\":1000000,\"viewtype\":\"File\",\"filename\":\"test.bin\"}"
+        );
+        assert_eq!(
+            PreMsgMetadata {
+                size: 5_342_765,
+                viewtype: Viewtype::Image,
+                filename: "vacation.png".to_string(),
+                dimensions: Some((1080, 1920)),
+                duration: None,
+            }
+            .to_header_value()?,
+            "{\"size\":5342765,\"viewtype\":\"Image\",\"filename\":\"vacation.png\",\"dimensions\":[1080,1920]}"
+        );
+        assert_eq!(
+            PreMsgMetadata {
+                size: 5_000,
+                viewtype: Viewtype::Audio,
+                filename: "audio-DD-MM-YY.ogg".to_string(),
+                dimensions: None,
+                duration: Some(152_310),
+            }
+            .to_header_value()?,
+            "{\"size\":5000,\"viewtype\":\"Audio\",\"filename\":\"audio-DD-MM-YY.ogg\",\"duration\":152310}"
+        );
+
+        Ok(())
+    }
+
+    /// Test that deserialisation from expected format works
+    /// This test will become important for compatibility between versions in the future
+    #[test]
+    fn test_deserialize_from_header() -> Result<()> {
+        assert_eq!(
+            serde_json::from_str::<PreMsgMetadata>(
+                "{\"size\":1000000,\"viewtype\":\"File\",\"filename\":\"test.bin\",\"dimensions\":null,\"duration\":null}"
+            )?,
+            PreMsgMetadata {
+                size: 1_000_000,
+                viewtype: Viewtype::File,
+                filename: "test.bin".to_string(),
+                dimensions: None,
+                duration: None,
+            }
+        );
+        assert_eq!(
+            serde_json::from_str::<PreMsgMetadata>(
+                "{\"size\":5342765,\"viewtype\":\"Image\",\"filename\":\"vacation.png\",\"dimensions\":[1080,1920]}"
+            )?,
+            PreMsgMetadata {
+                size: 5_342_765,
+                viewtype: Viewtype::Image,
+                filename: "vacation.png".to_string(),
+                dimensions: Some((1080, 1920)),
+                duration: None,
+            }
+        );
+        assert_eq!(
+            serde_json::from_str::<PreMsgMetadata>(
+                "{\"size\":5000,\"viewtype\":\"Audio\",\"filename\":\"audio-DD-MM-YY.ogg\",\"duration\":152310}"
+            )?,
+            PreMsgMetadata {
+                size: 5_000,
+                viewtype: Viewtype::Audio,
+                filename: "audio-DD-MM-YY.ogg".to_string(),
+                dimensions: None,
+                duration: Some(152_310),
+            }
+        );
+
+        Ok(())
+    }
+}

src/headerdef.rs

@@ -102,6 +102,21 @@ pub enum HeaderDef {
     /// used to encrypt and decrypt messages.
     /// This secret is sent to a new member in the member-addition message.
     ChatBroadcastSecret,
+    /// A message with a large attachment is split into two MIME messages:
+    /// A pre-message, which contains everything but the attachment,
+    /// and a Post-Message.
+    /// The Pre-Message gets a `Chat-Post-Message-Id` header
+    /// referencing the Post-Message's rfc724_mid.
+    ChatPostMessageId,
+
+    /// Announce Post-Message metadata in a Pre-Message.
+    /// contains serialized PreMsgMetadata struct
+    ChatPostMessageMetadata,
+
+    /// This message is preceded by a Pre-Message
+    /// and thus this message can be skipped while fetching messages.
+    /// This is a cleartext / unproteced header.
+    ChatIsPostMessage,
 
     /// [Autocrypt](https://autocrypt.org/) header.
     Autocrypt,
@@ -147,6 +162,9 @@ pub enum HeaderDef {
 
 impl HeaderDef {
     /// Returns the corresponding header string.
+    ///
+    /// Format is lower-kebab-case for easy comparisons.
+    /// This method is used in message receiving and testing.
     pub fn get_headername(&self) -> &'static str {
         self.into()
     }

src/imap.rs

@@ -23,7 +23,6 @@ use num_traits::FromPrimitive;
 use ratelimit::Ratelimit;
 use url::Url;
 
-use crate::calls::{create_fallback_ice_servers, create_ice_servers_from_metadata};
 use crate::chat::{self, ChatId, ChatIdBlocked, add_device_msg};
 use crate::chatlist_events;
 use crate::config::Config;
@@ -48,6 +47,10 @@ use crate::tools::{self, create_id, duration_to_str, time};
 use crate::transport::{
     ConfiguredLoginParam, ConfiguredServerLoginParam, prioritize_server_login_params,
 };
+use crate::{
+    calls::{create_fallback_ice_servers, create_ice_servers_from_metadata},
+    download::MAX_FETCH_MSG_SIZE,
+};
 
 pub(crate) mod capabilities;
 mod client;
@@ -67,7 +70,6 @@ const RFC724MID_UID: &str = "(UID BODY.PEEK[HEADER.FIELDS (\
                              X-MICROSOFT-ORIGINAL-MESSAGE-ID\
                              )])";
 const BODY_FULL: &str = "(FLAGS BODY.PEEK[])";
-const BODY_PARTIAL: &str = "(FLAGS RFC822.SIZE BODY.PEEK[HEADER])";
 
 #[derive(Debug)]
 pub(crate) struct Imap {
@@ -521,6 +523,7 @@ impl Imap {
         &mut self,
         context: &Context,
         session: &mut Session,
+        is_background_fetch: bool,
         watch_folder: &str,
         folder_meaning: FolderMeaning,
     ) -> Result<()> {
@@ -530,7 +533,13 @@ impl Imap {
         }
 
         let msgs_fetched = self
-            .fetch_new_messages(context, session, watch_folder, folder_meaning)
+            .fetch_new_messages(
+                context,
+                session,
+                is_background_fetch,
+                watch_folder,
+                folder_meaning,
+            )
             .await
             .context("fetch_new_messages")?;
         if msgs_fetched && context.get_config_delete_device_after().await?.is_some() {
@@ -556,6 +565,7 @@ impl Imap {
         &mut self,
         context: &Context,
         session: &mut Session,
+        is_background_fetch: bool,
         folder: &str,
         folder_meaning: FolderMeaning,
     ) -> Result<bool> {
@@ -583,7 +593,13 @@ impl Imap {
         let mut read_cnt = 0;
         loop {
             let (n, fetch_more) = self
-                .fetch_new_msg_batch(context, session, folder, folder_meaning)
+                .fetch_new_msg_batch(
+                    context,
+                    session,
+                    is_background_fetch,
+                    folder,
+                    folder_meaning,
+                )
                 .await?;
             read_cnt += n;
             if !fetch_more {
@@ -597,6 +613,7 @@ impl Imap {
         &mut self,
         context: &Context,
         session: &mut Session,
+        is_background_fetch: bool,
         folder: &str,
         folder_meaning: FolderMeaning,
     ) -> Result<(usize, bool)> {
@@ -615,12 +632,23 @@ impl Imap {
             .context("prefetch")?;
         let read_cnt = msgs.len();
 
-        let download_limit = context.download_limit().await?;
-        let mut uids_fetch = Vec::<(u32, bool /* partially? */)>::with_capacity(msgs.len() + 1);
+        let mut uids_fetch = Vec::<u32>::with_capacity(msgs.len() + 1);
+        let mut available_post_msgs = Vec::<String>::with_capacity(msgs.len());
+        let mut download_when_normal_starts = Vec::<String>::with_capacity(msgs.len());
         let mut uid_message_ids = BTreeMap::new();
         let mut largest_uid_skipped = None;
         let delete_target = context.get_delete_msgs_target().await?;
 
+        let download_limit = {
+            let download_limit: Option<u32> =
+                context.get_config_parsed(Config::DownloadLimit).await?;
+            if download_limit == Some(0) {
+                None
+            } else {
+                download_limit
+            }
+        };
+
         // Store the info about IMAP messages in the database.
         for (uid, ref fetch_response) in msgs {
             let headers = match get_fetch_headers(fetch_response) {
@@ -632,6 +660,9 @@ impl Imap {
             };
 
             let message_id = prefetch_get_message_id(&headers);
+            let size = fetch_response
+                .size
+                .context("imap fetch response does not contain size")?;
 
             // Determine the target folder where the message should be moved to.
             //
@@ -706,14 +737,47 @@ impl Imap {
                 )
                 .await.context("prefetch_should_download")?
             {
-                match download_limit {
-                    Some(download_limit) => uids_fetch.push((
-                        uid,
-                        fetch_response.size.unwrap_or_default() > download_limit,
-                    )),
-                    None => uids_fetch.push((uid, false)),
+                let fetch_now: bool = if headers
+                    .get_header_value(HeaderDef::ChatIsPostMessage)
+                    .is_some()
+                {
+                    info!(context, "{} is a post message", message_id.clone());
+                    // This is a Post-Message
+                    available_post_msgs.push(message_id.clone());
+
+                    // whether it fits download size limit
+                    if download_limit.is_none_or(|download_limit| size < download_limit) {
+                        if is_background_fetch {
+                            download_when_normal_starts.push(message_id.clone());
+                            false
+                        } else {
+                            true
+                        }
+                    } else {
+                        false
+                    }
+                } else {
+                    info!(context, "{} is not a post message", message_id.clone());
+                    // This is not a Post-Message
+                    if is_background_fetch {
+                        if size < MAX_FETCH_MSG_SIZE {
+                            // may be a Pre-Message or a small normal message, fetch now
+                            true
+                        } else {
+                            // This is e.g. a classical email or large webxdc status update
+                            // Queue for full download, in order to prevent missing messages
+                            download_when_normal_starts.push(message_id.clone());
+                            false
+                        }
+                    } else {
+                        true
+                    }
+                };
+
+                if fetch_now {
+                    uids_fetch.push(uid);
+                    uid_message_ids.insert(uid, message_id);
                 }
-                uid_message_ids.insert(uid, message_id);
             } else {
                 largest_uid_skipped = Some(uid);
             }
@@ -747,29 +811,10 @@ impl Imap {
         };
 
         let actually_download_messages_future = async {
-            let sender = sender;
-            let mut uids_fetch_in_batch = Vec::with_capacity(max(uids_fetch.len(), 1));
-            let mut fetch_partially = false;
-            uids_fetch.push((0, !uids_fetch.last().unwrap_or(&(0, false)).1));
-            for (uid, fp) in uids_fetch {
-                if fp != fetch_partially {
-                    session
-                        .fetch_many_msgs(
-                            context,
-                            folder,
-                            uids_fetch_in_batch.split_off(0),
-                            &uid_message_ids,
-                            fetch_partially,
-                            sender.clone(),
-                        )
-                        .await
-                        .context("fetch_many_msgs")?;
-                    fetch_partially = fp;
-                }
-                uids_fetch_in_batch.push(uid);
-            }
-
-            anyhow::Ok(())
+            session
+                .fetch_many_msgs(context, folder, uids_fetch, &uid_message_ids, sender)
+                .await
+                .context("fetch_many_msgs")
         };
 
         let (largest_uid_fetched, fetch_res) =
@@ -804,6 +849,31 @@ impl Imap {
 
         chat::mark_old_messages_as_noticed(context, received_msgs).await?;
 
+        // TODO: is there correct place for this?
+        if fetch_res.is_ok() {
+            info!(
+                context,
+                "available_post_msgs: {}, download_when_normal_starts: {}",
+                available_post_msgs.len(),
+                download_when_normal_starts.len()
+            );
+            for rfc724_mid in available_post_msgs {
+                context
+                    .sql
+                    .insert("INSERT INTO available_post_msgs VALUES (?)", (rfc724_mid,))
+                    .await?;
+            }
+            for rfc724_mid in download_when_normal_starts {
+                context
+                    .sql
+                    .insert(
+                        "INSERT INTO download (rfc724_mid) VALUES (?)",
+                        (rfc724_mid,),
+                    )
+                    .await?;
+            }
+        }
+
         // Now fail if fetching failed, so we will
         // establish a new session if this one is broken.
         fetch_res?;
@@ -1373,7 +1443,6 @@ impl Session {
         folder: &str,
         request_uids: Vec<u32>,
         uid_message_ids: &BTreeMap<u32, String>,
-        fetch_partially: bool,
         received_msgs_channel: Sender<(u32, Option<ReceivedMsg>)>,
     ) -> Result<()> {
         if request_uids.is_empty() {
@@ -1381,25 +1450,10 @@ impl Session {
         }
 
         for (request_uids, set) in build_sequence_sets(&request_uids)? {
-            info!(
-                context,
-                "Starting a {} FETCH of message set \"{}\".",
-                if fetch_partially { "partial" } else { "full" },
-                set
-            );
-            let mut fetch_responses = self
-                .uid_fetch(
-                    &set,
-                    if fetch_partially {
-                        BODY_PARTIAL
-                    } else {
-                        BODY_FULL
-                    },
-                )
-                .await
-                .with_context(|| {
-                    format!("fetching messages {} from folder \"{}\"", &set, folder)
-                })?;
+            info!(context, "Starting a full FETCH of message set \"{}\".", set);
+            let mut fetch_responses = self.uid_fetch(&set, BODY_FULL).await.with_context(|| {
+                format!("fetching messages {} from folder \"{}\"", &set, folder)
+            })?;
 
             // Map from UIDs to unprocessed FETCH results. We put unprocessed FETCH results here
             // when we want to process other messages first.
@@ -1456,11 +1510,7 @@ impl Session {
                 count += 1;
 
                 let is_deleted = fetch_response.flags().any(|flag| flag == Flag::Deleted);
-                let (body, partial) = if fetch_partially {
-                    (fetch_response.header(), fetch_response.size) // `BODY.PEEK[HEADER]` goes to header() ...
-                } else {
-                    (fetch_response.body(), None) // ... while `BODY.PEEK[]` goes to body() - and includes header()
-                };
+                let body = fetch_response.body();
 
                 if is_deleted {
                     info!(context, "Not processing deleted msg {}.", request_uid);
@@ -1494,7 +1544,7 @@ impl Session {
                     context,
                     "Passing message UID {} to receive_imf().", request_uid
                 );
-                let res = receive_imf_inner(context, rfc724_mid, body, is_seen, partial).await;
+                let res = receive_imf_inner(context, rfc724_mid, body, is_seen).await;
                 let received_msg = match res {
                     Err(err) => {
                         warn!(context, "receive_imf error: {err:#}.");

src/imap/scan_folders.rs

@@ -76,7 +76,7 @@ impl Imap {
                 && folder_meaning != FolderMeaning::Trash
                 && folder_meaning != FolderMeaning::Unknown
             {
-                self.fetch_move_delete(context, session, folder.name(), folder_meaning)
+                self.fetch_move_delete(context, session, false, folder.name(), folder_meaning)
                     .await
                     .context("Can't fetch new msgs in scanned folder")
                     .log_err(context)

src/imap/session.rs

@@ -17,6 +17,7 @@ use crate::tools;
 /// - Chat-Version to check if a message is a chat message
 /// - Autocrypt-Setup-Message to check if a message is an autocrypt setup message,
 ///   not necessarily sent by Delta Chat.
+/// - Chat-Is-Post-Message to skip it in background fetch or when it is too large
 const PREFETCH_FLAGS: &str = "(UID INTERNALDATE RFC822.SIZE BODY.PEEK[HEADER.FIELDS (\
                               MESSAGE-ID \
                               DATE \
@@ -24,6 +25,7 @@ const PREFETCH_FLAGS: &str = "(UID INTERNALDATE RFC822.SIZE BODY.PEEK[HEADER.FIE
                               FROM \
                               IN-REPLY-TO REFERENCES \
                               CHAT-VERSION \
+                              CHAT-IS-POST-MESSAGE \
                               AUTO-SUBMITTED \
                               AUTOCRYPT-SETUP-MESSAGE\
                               )])";

src/imex.rs

@@ -783,6 +783,13 @@ async fn export_database(
             let res = conn
                 .query_row("SELECT sqlcipher_export('backup')", [], |_row| Ok(()))
                 .context("failed to export to attached backup database");
+            // This option is device/client specific, so we reset it on backup.
+            // The test for this is tests::pre_messages::additional_text::test_disable_option_is_exluded_from_backup
+            conn.execute(
+                "UPDATE backup.config SET value='0' WHERE keyname=?;",
+                [Config::HidePreMessageMetadataText.to_string()],
+            )
+            .ok();
             conn.execute(
                 "UPDATE backup.config SET value='0' WHERE keyname='verified_one_on_one_chats';",
                 [],

src/internals_for_benches.rs

@@ -21,7 +21,7 @@ pub async fn store_self_keypair(context: &Context, keypair: &KeyPair) -> Result<
 }
 
 pub async fn parse_and_get_text(context: &Context, imf_raw: &[u8]) -> Result<String> {
-    let mime_parser = MimeMessage::from_bytes(context, imf_raw, None).await?;
+    let mime_parser = MimeMessage::from_bytes(context, imf_raw).await?;
     Ok(mime_parser.parts.into_iter().next().unwrap().msg)
 }
 

src/message.rs

@@ -8,6 +8,9 @@ use std::str;
 use anyhow::{Context as _, Result, ensure, format_err};
 use deltachat_contact_tools::{VcardContact, parse_vcard};
 use deltachat_derive::{FromSql, ToSql};
+use humansize::BINARY;
+use humansize::format_size;
+use num_traits::FromPrimitive;
 use serde::{Deserialize, Serialize};
 use tokio::{fs, io};
 
@@ -425,6 +428,10 @@ pub struct Message {
     pub(crate) ephemeral_timer: EphemeralTimer,
     pub(crate) ephemeral_timestamp: i64,
     pub(crate) text: String,
+    /// Text that is added to the end of Message.text
+    ///
+    /// Currently used for adding the download information on pre-messages
+    pub(crate) additional_text: String,
 
     /// Message subject.
     ///
@@ -483,7 +490,7 @@ impl Message {
             !id.is_special(),
             "Can not load special message ID {id} from DB"
         );
-        let msg = context
+        let mut msg = context
             .sql
             .query_row_optional(
                 concat!(
@@ -565,6 +572,7 @@ impl Message {
                         original_msg_id: row.get("original_msg_id")?,
                         mime_modified: row.get("mime_modified")?,
                         text,
+                        additional_text: String::new(),
                         subject: row.get("subject")?,
                         param: row.get::<_, String>("param")?.parse().unwrap_or_default(),
                         hidden: row.get("hidden")?,
@@ -579,9 +587,53 @@ impl Message {
             .await
             .with_context(|| format!("failed to load message {id} from the database"))?;
 
+        if let Some(msg) = &mut msg {
+            msg.additional_text =
+                Self::get_additional_text(context, msg.download_state, &msg.param).await?;
+        }
+
         Ok(msg)
     }
 
+    /// Returns additional text which is appended to the message's text field
+    /// when it is loaded from the database.
+    /// Currently this is used to add infomation to pre-messages of what the download will be and how large it is
+    async fn get_additional_text(
+        context: &Context,
+        download_state: DownloadState,
+        param: &Params,
+    ) -> Result<String> {
+        if download_state != DownloadState::Done {
+            let hide_pre_message_metadata = context
+                .get_config_bool(Config::HidePreMessageMetadataText)
+                .await?;
+            if !hide_pre_message_metadata {
+                let file_size = param
+                    .get(Param::PostMessageFileBytes)
+                    .and_then(|s| s.parse().ok())
+                    .map(|file_size: usize| format_size(file_size, BINARY))
+                    .unwrap_or("?".to_owned());
+                let viewtype = param
+                    .get_i64(Param::PostMessageViewtype)
+                    .and_then(Viewtype::from_i64)
+                    .unwrap_or(Viewtype::Unknown);
+                let file_name = param
+                    .get(Param::Filename)
+                    .map(sanitize_filename)
+                    .unwrap_or("?".to_owned());
+
+                return match viewtype {
+                    Viewtype::File => Ok(format!(" [{file_name} - {file_size}]")),
+                    _ => {
+                        let translated_viewtype = viewtype.to_locale_string(context).await;
+                        Ok(format!(" [{translated_viewtype} - {file_size}]"))
+                    }
+                };
+            }
+        }
+        Ok(String::new())
+    }
+
     /// Returns the MIME type of an attached file if it exists.
     ///
     /// If the MIME type is not known, the function guesses the MIME type
@@ -764,7 +816,7 @@ impl Message {
 
     /// Returns the text of the message.
     pub fn get_text(&self) -> String {
-        self.text.clone()
+        self.text.clone() + &self.additional_text
     }
 
     /// Returns message subject.
@@ -786,7 +838,18 @@ impl Message {
     }
 
     /// Returns the size of the file in bytes, if applicable.
+    /// If message is a pre-message, then this returns size of the to be downloaded file.
     pub async fn get_filebytes(&self, context: &Context) -> Result<Option<u64>> {
+        // if download state is not downloaded then return value from from params metadata
+        if self.download_state != DownloadState::Done {
+            if let Some(file_size) = self
+                .param
+                .get(Param::PostMessageFileBytes)
+                .and_then(|s| s.parse().ok())
+            {
+                return Ok(Some(file_size));
+            }
+        }
         if let Some(path) = self.param.get_file_path(context)? {
             Ok(Some(get_filebytes(context, &path).await.with_context(
                 || format!("failed to get {} size in bytes", path.display()),
@@ -796,6 +859,21 @@ impl Message {
         }
     }
 
+    /// If message is a Pre-Message,
+    /// then this returns the viewtype it will have when it is downloaded.
+    pub fn get_post_message_viewtype(&self) -> Option<Viewtype> {
+        if self.download_state != DownloadState::Done {
+            if let Some(viewtype) = self
+                .param
+                .get_i64(Param::PostMessageViewtype)
+                .and_then(Viewtype::from_i64)
+            {
+                return Some(viewtype);
+            }
+        }
+        None
+    }
+
     /// Returns width of associated image or video file.
     pub fn get_width(&self) -> i32 {
         self.param.get_int(Param::Width).unwrap_or_default()
@@ -1676,9 +1754,17 @@ pub async fn delete_msgs_ex(
         let update_db = |trans: &mut rusqlite::Transaction| {
             trans.execute(
                 "UPDATE imap SET target=? WHERE rfc724_mid=?",
-                (target, msg.rfc724_mid),
+                (target, &msg.rfc724_mid),
             )?;
             trans.execute("DELETE FROM smtp WHERE msg_id=?", (msg_id,))?;
+            trans.execute(
+                "DELETE FROM download WHERE rfc724_mid=?",
+                (&msg.rfc724_mid,),
+            )?;
+            trans.execute(
+                "DELETE FROM available_post_msgs WHERE rfc724_mid=?",
+                (&msg.rfc724_mid,),
+            )?;
             Ok(())
         };
         if let Err(e) = context.sql.transaction(update_db).await {
@@ -1746,7 +1832,6 @@ pub async fn markseen_msgs(context: &Context, msg_ids: Vec<MsgId>) -> Result<()>
                 "SELECT
                     m.chat_id AS chat_id,
                     m.state AS state,
-                    m.download_state as download_state,
                     m.ephemeral_timer AS ephemeral_timer,
                     m.param AS param,
                     m.from_id AS from_id,
@@ -1759,7 +1844,6 @@ pub async fn markseen_msgs(context: &Context, msg_ids: Vec<MsgId>) -> Result<()>
                 |row| {
                     let chat_id: ChatId = row.get("chat_id")?;
                     let state: MessageState = row.get("state")?;
-                    let download_state: DownloadState = row.get("download_state")?;
                     let param: Params = row.get::<_, String>("param")?.parse().unwrap_or_default();
                     let from_id: ContactId = row.get("from_id")?;
                     let rfc724_mid: String = row.get("rfc724_mid")?;
@@ -1771,7 +1855,6 @@ pub async fn markseen_msgs(context: &Context, msg_ids: Vec<MsgId>) -> Result<()>
                             id,
                             chat_id,
                             state,
-                            download_state,
                             param,
                             from_id,
                             rfc724_mid,
@@ -1804,7 +1887,6 @@ pub async fn markseen_msgs(context: &Context, msg_ids: Vec<MsgId>) -> Result<()>
             id,
             curr_chat_id,
             curr_state,
-            curr_download_state,
             curr_param,
             curr_from_id,
             curr_rfc724_mid,
@@ -1814,14 +1896,7 @@ pub async fn markseen_msgs(context: &Context, msg_ids: Vec<MsgId>) -> Result<()>
         _curr_ephemeral_timer,
     ) in msgs
     {
-        if curr_download_state != DownloadState::Done {
-            if curr_state == MessageState::InFresh {
-                // Don't mark partially downloaded messages as seen or send a read receipt since
-                // they are not really seen by the user.
-                update_msg_state(context, id, MessageState::InNoticed).await?;
-                updated_chat_ids.insert(curr_chat_id);
-            }
-        } else if curr_state == MessageState::InFresh || curr_state == MessageState::InNoticed {
+        if curr_state == MessageState::InFresh || curr_state == MessageState::InNoticed {
             update_msg_state(context, id, MessageState::InSeen).await?;
             info!(context, "Seen message {}.", id);
 

src/message/message_tests.rs

@@ -326,112 +326,6 @@ async fn test_markseen_msgs() -> Result<()> {
     Ok(())
 }
 
-#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn test_markseen_not_downloaded_msg() -> Result<()> {
-    let mut tcm = TestContextManager::new();
-    let alice = &tcm.alice().await;
-    alice.set_config(Config::DownloadLimit, Some("1")).await?;
-    let bob = &tcm.bob().await;
-    let bob_chat_id = bob.create_chat(alice).await.id;
-    alice.create_chat(bob).await; // Make sure the chat is accepted.
-
-    tcm.section("Bob sends a large message to Alice");
-    let file_bytes = include_bytes!("../../test-data/image/screenshot.png");
-    let mut msg = Message::new(Viewtype::Image);
-    msg.set_file_from_bytes(bob, "a.jpg", file_bytes, None)?;
-    let sent_msg = bob.send_msg(bob_chat_id, &mut msg).await;
-
-    tcm.section("Alice receives a large message from Bob");
-    let msg = alice.recv_msg(&sent_msg).await;
-    assert_eq!(msg.download_state, DownloadState::Available);
-    assert!(!msg.param.get_bool(Param::WantsMdn).unwrap_or_default());
-    assert_eq!(msg.state, MessageState::InFresh);
-    markseen_msgs(alice, vec![msg.id]).await?;
-    // A not downloaded message can be seen only if it's seen on another device.
-    assert_eq!(msg.id.get_state(alice).await?, MessageState::InNoticed);
-    // Marking the message as seen again is a no op.
-    markseen_msgs(alice, vec![msg.id]).await?;
-    assert_eq!(msg.id.get_state(alice).await?, MessageState::InNoticed);
-
-    msg.id
-        .update_download_state(alice, DownloadState::InProgress)
-        .await?;
-    markseen_msgs(alice, vec![msg.id]).await?;
-    assert_eq!(msg.id.get_state(alice).await?, MessageState::InNoticed);
-    msg.id
-        .update_download_state(alice, DownloadState::Failure)
-        .await?;
-    markseen_msgs(alice, vec![msg.id]).await?;
-    assert_eq!(msg.id.get_state(alice).await?, MessageState::InNoticed);
-    msg.id
-        .update_download_state(alice, DownloadState::Undecipherable)
-        .await?;
-    markseen_msgs(alice, vec![msg.id]).await?;
-    assert_eq!(msg.id.get_state(alice).await?, MessageState::InNoticed);
-
-    assert!(
-        !alice
-            .sql
-            .exists("SELECT COUNT(*) FROM smtp_mdns", ())
-            .await?
-    );
-
-    alice.set_config(Config::DownloadLimit, None).await?;
-    // Let's assume that Alice and Bob resolved the problem with encryption.
-    let old_msg = msg;
-    let msg = alice.recv_msg(&sent_msg).await;
-    assert_eq!(msg.chat_id, old_msg.chat_id);
-    assert_eq!(msg.download_state, DownloadState::Done);
-    assert!(msg.param.get_bool(Param::WantsMdn).unwrap_or_default());
-    assert!(msg.get_showpadlock());
-    // The message state mustn't be downgraded to `InFresh`.
-    assert_eq!(msg.state, MessageState::InNoticed);
-    markseen_msgs(alice, vec![msg.id]).await?;
-    let msg = Message::load_from_db(alice, msg.id).await?;
-    assert_eq!(msg.state, MessageState::InSeen);
-    assert_eq!(
-        alice
-            .sql
-            .count("SELECT COUNT(*) FROM smtp_mdns", ())
-            .await?,
-        1
-    );
-    Ok(())
-}
-
-#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn test_msg_seen_on_imap_when_downloaded() -> Result<()> {
-    let mut tcm = TestContextManager::new();
-    let alice = &tcm.alice().await;
-    alice.set_config(Config::DownloadLimit, Some("1")).await?;
-    let bob = &tcm.bob().await;
-    let bob_chat_id = tcm.send_recv_accept(alice, bob, "hi").await.chat_id;
-
-    let file_bytes = include_bytes!("../../test-data/image/screenshot.png");
-    let mut msg = Message::new(Viewtype::Image);
-    msg.set_file_from_bytes(bob, "a.jpg", file_bytes, None)?;
-    let sent_msg = bob.send_msg(bob_chat_id, &mut msg).await;
-    let msg = alice.recv_msg(&sent_msg).await;
-    assert_eq!(msg.download_state, DownloadState::Available);
-    assert_eq!(msg.state, MessageState::InFresh);
-
-    alice.set_config(Config::DownloadLimit, None).await?;
-    let seen = true;
-    let rcvd_msg = receive_imf(alice, sent_msg.payload().as_bytes(), seen)
-        .await
-        .unwrap()
-        .unwrap();
-    assert_eq!(rcvd_msg.chat_id, msg.chat_id);
-    let msg = Message::load_from_db(alice, *rcvd_msg.msg_ids.last().unwrap())
-        .await
-        .unwrap();
-    assert_eq!(msg.download_state, DownloadState::Done);
-    assert!(msg.param.get_bool(Param::WantsMdn).unwrap_or_default());
-    assert!(msg.get_showpadlock());
-    assert_eq!(msg.state, MessageState::InSeen);
-    Ok(())
-}
-
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_get_state() -> Result<()> {
     let alice = TestContext::new_alice().await;

src/mimefactory.rs

@@ -21,6 +21,7 @@ use crate::constants::{ASM_SUBJECT, BROADCAST_INCOMPATIBILITY_MSG};
 use crate::constants::{Chattype, DC_FROM_HANDSHAKE};
 use crate::contact::{Contact, ContactId, Origin};
 use crate::context::Context;
+use crate::download::pre_msg_metadata::PreMsgMetadata;
 use crate::e2ee::EncryptHelper;
 use crate::ensure_and_debug_assert;
 use crate::ephemeral::Timer as EphemeralTimer;
@@ -59,6 +60,15 @@ pub enum Loaded {
     },
 }
 
+#[derive(Debug, Clone, PartialEq)]
+pub enum PreMessageMode {
+    /// adds the Chat-Is-Post-Message header in unprotected part
+    PostMessage,
+    /// adds the Chat-Post-Message-ID header to protected part
+    /// also adds metadata and explicitly excludes attachment
+    PreMessage { post_msg_rfc724_mid: String },
+}
+
 /// Helper to construct mime messages.
 #[derive(Debug, Clone)]
 pub struct MimeFactory {
@@ -146,6 +156,9 @@ pub struct MimeFactory {
 
     /// This field is used to sustain the topic id of webxdcs needed for peer channels.
     webxdc_topic: Option<TopicId>,
+
+    /// This field is used when this is either a pre-message or a Post-Message.
+    pre_message_mode: Option<PreMessageMode>,
 }
 
 /// Result of rendering a message, ready to be submitted to a send job.
@@ -500,6 +513,7 @@ impl MimeFactory {
             sync_ids_to_delete: None,
             attach_selfavatar,
             webxdc_topic,
+            pre_message_mode: None,
         };
         Ok(factory)
     }
@@ -548,6 +562,7 @@ impl MimeFactory {
             sync_ids_to_delete: None,
             attach_selfavatar: false,
             webxdc_topic: None,
+            pre_message_mode: None,
         };
 
         Ok(res)
@@ -779,7 +794,10 @@ impl MimeFactory {
         headers.push(("Date", mail_builder::headers::raw::Raw::new(date).into()));
 
         let rfc724_mid = match &self.loaded {
-            Loaded::Message { msg, .. } => msg.rfc724_mid.clone(),
+            Loaded::Message { msg, .. } => match &self.pre_message_mode {
+                Some(PreMessageMode::PreMessage { .. }) => create_outgoing_rfc724_mid(),
+                _ => msg.rfc724_mid.clone(),
+            },
             Loaded::Mdn { .. } => create_outgoing_rfc724_mid(),
         };
         headers.push((
@@ -893,7 +911,7 @@ impl MimeFactory {
             ));
         }
 
-        let is_encrypted = self.encryption_pubkeys.is_some();
+        let is_encrypted = self.will_be_encrypted();
 
         // Add ephemeral timer for non-MDN messages.
         // For MDNs it does not matter because they are not visible
@@ -978,6 +996,22 @@ impl MimeFactory {
             "MIME-Version",
             mail_builder::headers::raw::Raw::new("1.0").into(),
         ));
+
+        if self.pre_message_mode == Some(PreMessageMode::PostMessage) {
+            unprotected_headers.push((
+                "Chat-Is-Post-Message",
+                mail_builder::headers::raw::Raw::new("1").into(),
+            ));
+        } else if let Some(PreMessageMode::PreMessage {
+            post_msg_rfc724_mid,
+        }) = self.pre_message_mode.clone()
+        {
+            protected_headers.push((
+                "Chat-Post-Message-ID",
+                mail_builder::headers::message_id::MessageId::new(post_msg_rfc724_mid).into(),
+            ));
+        }
+
         for header @ (original_header_name, _header_value) in &headers {
             let header_name = original_header_name.to_lowercase();
             if header_name == "message-id" {
@@ -1119,6 +1153,10 @@ impl MimeFactory {
                         for (addr, key) in &encryption_pubkeys {
                             let fingerprint = key.dc_fingerprint().hex();
                             let cmd = msg.param.get_cmd();
+                            if self.pre_message_mode == Some(PreMessageMode::PostMessage) {
+                                continue;
+                            }
+
                             let should_do_gossip = cmd == SystemMessage::MemberAddedToGroup
                                 || cmd == SystemMessage::SecurejoinMessage
                                 || multiple_recipients && {
@@ -1875,8 +1913,20 @@ impl MimeFactory {
 
         // add attachment part
         if msg.viewtype.has_file() {
-            let file_part = build_body_file(context, &msg).await?;
-            parts.push(file_part);
+            if let Some(PreMessageMode::PreMessage { .. }) = self.pre_message_mode {
+                let Some(metadata) = PreMsgMetadata::from_msg(context, &msg).await? else {
+                    bail!("failed to generate metadata for pre-message")
+                };
+
+                headers.push((
+                    HeaderDef::ChatPostMessageMetadata.into(),
+                    mail_builder::headers::raw::Raw::new(metadata.to_header_value()?).into(),
+                ));
+                // TODO: generate thumbnail and attach it instead (if it makes sense)
+            } else {
+                let file_part = build_body_file(context, &msg).await?;
+                parts.push(file_part);
+            }
         }
 
         if let Some(msg_kml_part) = self.get_message_kml_part() {
@@ -1921,6 +1971,8 @@ impl MimeFactory {
             }
         }
 
+        self.attach_selfavatar =
+            self.attach_selfavatar && self.pre_message_mode != Some(PreMessageMode::PostMessage);
         if self.attach_selfavatar {
             match context.get_config(Config::Selfavatar).await? {
                 Some(path) => match build_avatar_file(context, &path).await {
@@ -1990,6 +2042,20 @@ impl MimeFactory {
 
         Ok(message)
     }
+
+    pub fn will_be_encrypted(&self) -> bool {
+        self.encryption_pubkeys.is_some()
+    }
+
+    pub fn set_as_post_message(&mut self) {
+        self.pre_message_mode = Some(PreMessageMode::PostMessage);
+    }
+
+    pub fn set_as_pre_message_for(&mut self, post_message: &RenderedEmail) {
+        self.pre_message_mode = Some(PreMessageMode::PreMessage {
+            post_msg_rfc724_mid: post_message.rfc724_mid.clone(),
+        });
+    }
 }
 
 fn hidden_recipients() -> Address<'static> {

src/mimefactory/mimefactory_tests.rs

@@ -559,7 +559,7 @@ async fn test_render_reply() {
         "1.0"
     );
 
-    let _mime_msg = MimeMessage::from_bytes(context, rendered_msg.message.as_bytes(), None)
+    let _mime_msg = MimeMessage::from_bytes(context, rendered_msg.message.as_bytes())
         .await
         .unwrap();
 }
@@ -757,7 +757,7 @@ async fn test_protected_headers_directive() -> Result<()> {
     assert!(msg.get_showpadlock());
     assert!(sent.payload.contains("\r\nSubject: [...]\r\n"));
 
-    let mime = MimeMessage::from_bytes(&alice, sent.payload.as_bytes(), None).await?;
+    let mime = MimeMessage::from_bytes(&alice, sent.payload.as_bytes()).await?;
     let mut payload = str::from_utf8(&mime.decoded_data)?.splitn(2, "\r\n\r\n");
     let part = payload.next().unwrap();
     assert_eq!(
@@ -781,7 +781,7 @@ async fn test_hp_outer_headers() -> Result<()> {
             .await?;
         chat::send_text_msg(t, chat_id, "hi!".to_string()).await?;
         let sent_msg = t.pop_sent_msg().await;
-        let msg = MimeMessage::from_bytes(t, sent_msg.payload.as_bytes(), None).await?;
+        let msg = MimeMessage::from_bytes(t, sent_msg.payload.as_bytes()).await?;
         assert_eq!(msg.header_exists(HeaderDef::HpOuter), std_hp_composing);
         for hdr in ["Date", "From", "Message-ID"] {
             assert_eq!(
@@ -811,7 +811,7 @@ async fn test_dont_remove_self() -> Result<()> {
         .await;
 
     println!("{}", sent.payload);
-    let mime_message = MimeMessage::from_bytes(alice, sent.payload.as_bytes(), None)
+    let mime_message = MimeMessage::from_bytes(alice, sent.payload.as_bytes())
         .await
         .unwrap();
     assert!(!mime_message.header_exists(HeaderDef::ChatGroupPastMembers));

src/mimeparser.rs

@@ -23,6 +23,7 @@ use crate::contact::ContactId;
 use crate::context::Context;
 use crate::decrypt::{try_decrypt, validate_detached_signature};
 use crate::dehtml::dehtml;
+use crate::download::pre_msg_metadata::PreMsgMetadata;
 use crate::events::EventType;
 use crate::headerdef::{HeaderDef, HeaderDefMap};
 use crate::key::{self, DcKey, Fingerprint, SignedPublicKey, load_self_secret_keyring};
@@ -147,6 +148,23 @@ pub(crate) struct MimeMessage {
     /// Sender timestamp in secs since epoch. Allowed to be in the future due to unsynchronized
     /// clocks, but not too much.
     pub(crate) timestamp_sent: i64,
+
+    pub(crate) pre_message: Option<PreMessageMode>,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub(crate) enum PreMessageMode {
+    /// This is Post-Message
+    /// it replaces it's Pre-Message attachment if it exists already,
+    /// and if the Pre-Message does not exist it is treated as normal message
+    PostMessage,
+    /// This is a Pre-Message,
+    /// it adds a message preview for a Post-Message
+    /// and it is ignored if the Post-Message was downloaded already
+    PreMessage {
+        post_msg_rfc724_mid: String,
+        metadata: Option<PreMsgMetadata>,
+    },
 }
 
 #[derive(Debug, PartialEq)]
@@ -240,12 +258,9 @@ const MIME_AC_SETUP_FILE: &str = "application/autocrypt-setup";
 impl MimeMessage {
     /// Parse a mime message.
     ///
-    /// If `partial` is set, it contains the full message size in bytes.
-    pub(crate) async fn from_bytes(
-        context: &Context,
-        body: &[u8],
-        partial: Option<u32>,
-    ) -> Result<Self> {
+    /// This method has some side-effects,
+    /// such as saving blobs and saving found public keys to the database.
+    pub(crate) async fn from_bytes(context: &Context, body: &[u8]) -> Result<Self> {
         let mail = mailparse::parse_mail(body)?;
 
         let timestamp_rcvd = smeared_time(context);
@@ -302,7 +317,7 @@ impl MimeMessage {
                     );
                     (part, part.ctype.mimetype.parse::<Mime>()?)
                 } else {
-                    // If it's a partially fetched message, there are no subparts.
+                    // Not a valid signed message, handle it as plaintext.
                     (&mail, mimetype)
                 }
             } else {
@@ -352,6 +367,16 @@ impl MimeMessage {
 
         let mut aheader_values = mail.headers.get_all_values(HeaderDef::Autocrypt.into());
 
+        let mut pre_message = if mail
+            .headers
+            .get_header_value(HeaderDef::ChatIsPostMessage)
+            .is_some()
+        {
+            Some(PreMessageMode::PostMessage)
+        } else {
+            None
+        };
+
         let mail_raw; // Memory location for a possible decrypted message.
         let decrypted_msg; // Decrypted signed OpenPGP message.
         let secrets: Vec<String> = context
@@ -580,6 +605,37 @@ impl MimeMessage {
             signatures.clear();
         }
 
+        if let (Ok(mail), true) = (mail, is_encrypted) {
+            if let Some(post_msg_rfc724_mid) =
+                mail.headers.get_header_value(HeaderDef::ChatPostMessageId)
+            {
+                let post_msg_rfc724_mid = parse_message_id(&post_msg_rfc724_mid)?;
+                let metadata = if let Some(value) = mail
+                    .headers
+                    .get_header_value(HeaderDef::ChatPostMessageMetadata)
+                {
+                    match PreMsgMetadata::try_from_header_value(&value) {
+                        Ok(metadata) => Some(metadata),
+                        Err(error) => {
+                            error!(
+                                context,
+                                "failed to parse metadata header in pre-message: {error:#?}"
+                            );
+                            None
+                        }
+                    }
+                } else {
+                    warn!(context, "expected pre-message to have metadata header");
+                    None
+                };
+
+                pre_message = Some(PreMessageMode::PreMessage {
+                    post_msg_rfc724_mid,
+                    metadata,
+                });
+            }
+        }
+
         let mut parser = MimeMessage {
             parts: Vec::new(),
             headers,
@@ -615,33 +671,27 @@ impl MimeMessage {
             is_bot: None,
             timestamp_rcvd,
             timestamp_sent,
+            pre_message,
         };
 
-        match partial {
-            Some(org_bytes) => {
-                parser
-                    .create_stub_from_partial_download(context, org_bytes)
-                    .await?;
+        match mail {
+            Ok(mail) => {
+                parser.parse_mime_recursive(context, mail, false).await?;
             }
-            None => match mail {
-                Ok(mail) => {
-                    parser.parse_mime_recursive(context, mail, false).await?;
-                }
-                Err(err) => {
-                    let txt = "[This message cannot be decrypted.\n\n• It might already help to simply reply to this message and ask the sender to send the message again.\n\n• If you just re-installed Delta Chat then it is best if you re-setup Delta Chat now and choose \"Add as second device\" or import a backup.]";
+            Err(err) => {
+                let txt = "[This message cannot be decrypted.\n\n• It might already help to simply reply to this message and ask the sender to send the message again.\n\n• If you just re-installed Delta Chat then it is best if you re-setup Delta Chat now and choose \"Add as second device\" or import a backup.]";
 
-                    let part = Part {
-                        typ: Viewtype::Text,
-                        msg_raw: Some(txt.to_string()),
-                        msg: txt.to_string(),
-                        // Don't change the error prefix for now,
-                        // receive_imf.rs:lookup_chat_by_reply() checks it.
-                        error: Some(format!("Decrypting failed: {err:#}")),
-                        ..Default::default()
-                    };
-                    parser.do_add_single_part(part);
-                }
-            },
+                let part = Part {
+                    typ: Viewtype::Text,
+                    msg_raw: Some(txt.to_string()),
+                    msg: txt.to_string(),
+                    // Don't change the error prefix for now,
+                    // receive_imf.rs:lookup_chat_by_reply() checks it.
+                    error: Some(format!("Decrypting failed: {err:#}")),
+                    ..Default::default()
+                };
+                parser.do_add_single_part(part);
+            }
         };
 
         let is_location_only = parser.location_kml.is_some() && parser.parts.is_empty();

src/mimeparser/mimeparser_tests.rs

@@ -25,58 +25,54 @@ impl AvatarAction {
 async fn test_mimeparser_fromheader() {
     let ctx = TestContext::new_alice().await;
 
-    let mimemsg = MimeMessage::from_bytes(&ctx, b"From: g@c.de\n\nhi", None)
+    let mimemsg = MimeMessage::from_bytes(&ctx, b"From: g@c.de\n\nhi")
         .await
         .unwrap();
     let contact = mimemsg.from;
     assert_eq!(contact.addr, "g@c.de");
     assert_eq!(contact.display_name, None);
 
-    let mimemsg = MimeMessage::from_bytes(&ctx, b"From:   g@c.de  \n\nhi", None)
+    let mimemsg = MimeMessage::from_bytes(&ctx, b"From:   g@c.de  \n\nhi")
         .await
         .unwrap();
     let contact = mimemsg.from;
     assert_eq!(contact.addr, "g@c.de");
     assert_eq!(contact.display_name, None);
 
-    let mimemsg = MimeMessage::from_bytes(&ctx, b"From: <g@c.de>\n\nhi", None)
+    let mimemsg = MimeMessage::from_bytes(&ctx, b"From: <g@c.de>\n\nhi")
         .await
         .unwrap();
     let contact = mimemsg.from;
     assert_eq!(contact.addr, "g@c.de");
     assert_eq!(contact.display_name, None);
 
-    let mimemsg = MimeMessage::from_bytes(&ctx, b"From: Goetz C <g@c.de>\n\nhi", None)
+    let mimemsg = MimeMessage::from_bytes(&ctx, b"From: Goetz C <g@c.de>\n\nhi")
         .await
         .unwrap();
     let contact = mimemsg.from;
     assert_eq!(contact.addr, "g@c.de");
     assert_eq!(contact.display_name, Some("Goetz C".to_string()));
 
-    let mimemsg = MimeMessage::from_bytes(&ctx, b"From: \"Goetz C\" <g@c.de>\n\nhi", None)
+    let mimemsg = MimeMessage::from_bytes(&ctx, b"From: \"Goetz C\" <g@c.de>\n\nhi")
         .await
         .unwrap();
     let contact = mimemsg.from;
     assert_eq!(contact.addr, "g@c.de");
     assert_eq!(contact.display_name, Some("Goetz C".to_string()));
 
-    let mimemsg =
-        MimeMessage::from_bytes(&ctx, b"From: =?utf-8?q?G=C3=B6tz?= C <g@c.de>\n\nhi", None)
-            .await
-            .unwrap();
+    let mimemsg = MimeMessage::from_bytes(&ctx, b"From: =?utf-8?q?G=C3=B6tz?= C <g@c.de>\n\nhi")
+        .await
+        .unwrap();
     let contact = mimemsg.from;
     assert_eq!(contact.addr, "g@c.de");
     assert_eq!(contact.display_name, Some("Götz C".to_string()));
 
     // although RFC 2047 says, encoded-words shall not appear inside quoted-string,
     // this combination is used in the wild eg. by MailMate
-    let mimemsg = MimeMessage::from_bytes(
-        &ctx,
-        b"From: \"=?utf-8?q?G=C3=B6tz?= C\" <g@c.de>\n\nhi",
-        None,
-    )
-    .await
-    .unwrap();
+    let mimemsg =
+        MimeMessage::from_bytes(&ctx, b"From: \"=?utf-8?q?G=C3=B6tz?= C\" <g@c.de>\n\nhi")
+            .await
+            .unwrap();
     let contact = mimemsg.from;
     assert_eq!(contact.addr, "g@c.de");
     assert_eq!(contact.display_name, Some("Götz C".to_string()));
@@ -86,7 +82,7 @@ async fn test_mimeparser_fromheader() {
 async fn test_mimeparser_crash() {
     let context = TestContext::new_alice().await;
     let raw = include_bytes!("../../test-data/message/issue_523.txt");
-    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
 
@@ -98,7 +94,7 @@ async fn test_mimeparser_crash() {
 async fn test_get_rfc724_mid_exists() {
     let context = TestContext::new_alice().await;
     let raw = include_bytes!("../../test-data/message/mail_with_message_id.txt");
-    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
 
@@ -112,7 +108,7 @@ async fn test_get_rfc724_mid_exists() {
 async fn test_get_rfc724_mid_not_exists() {
     let context = TestContext::new_alice().await;
     let raw = include_bytes!("../../test-data/message/issue_523.txt");
-    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(mimeparser.get_rfc724_mid(), None);
@@ -324,7 +320,7 @@ async fn test_mailparse_0_16_0_panic() {
 
     // There should be an error, but no panic.
     assert!(
-        MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+        MimeMessage::from_bytes(&context.ctx, &raw[..])
             .await
             .is_err()
     );
@@ -341,7 +337,7 @@ async fn test_parse_first_addr() {
                     test1\n\
                     ";
 
-    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..], None).await;
+    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..]).await;
 
     assert!(mimeparser.is_err());
 }
@@ -356,7 +352,7 @@ async fn test_get_parent_timestamp() {
                     \n\
                     Some reply\n\
                     ";
-    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(
@@ -402,7 +398,7 @@ async fn test_mimeparser_with_context() {
                     --==break==--\n\
                     \n";
 
-    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
 
@@ -438,26 +434,26 @@ async fn test_mimeparser_with_avatars() {
     let t = TestContext::new_alice().await;
 
     let raw = include_bytes!("../../test-data/message/mail_attach_txt.eml");
-    let mimeparser = MimeMessage::from_bytes(&t, &raw[..], None).await.unwrap();
+    let mimeparser = MimeMessage::from_bytes(&t, &raw[..]).await.unwrap();
     assert_eq!(mimeparser.user_avatar, None);
     assert_eq!(mimeparser.group_avatar, None);
 
     let raw = include_bytes!("../../test-data/message/mail_with_user_avatar.eml");
-    let mimeparser = MimeMessage::from_bytes(&t, &raw[..], None).await.unwrap();
+    let mimeparser = MimeMessage::from_bytes(&t, &raw[..]).await.unwrap();
     assert_eq!(mimeparser.parts.len(), 1);
     assert_eq!(mimeparser.parts[0].typ, Viewtype::Text);
     assert!(mimeparser.user_avatar.unwrap().is_change());
     assert_eq!(mimeparser.group_avatar, None);
 
     let raw = include_bytes!("../../test-data/message/mail_with_user_avatar_deleted.eml");
-    let mimeparser = MimeMessage::from_bytes(&t, &raw[..], None).await.unwrap();
+    let mimeparser = MimeMessage::from_bytes(&t, &raw[..]).await.unwrap();
     assert_eq!(mimeparser.parts.len(), 1);
     assert_eq!(mimeparser.parts[0].typ, Viewtype::Text);
     assert_eq!(mimeparser.user_avatar, Some(AvatarAction::Delete));
     assert_eq!(mimeparser.group_avatar, None);
 
     let raw = include_bytes!("../../test-data/message/mail_with_user_and_group_avatars.eml");
-    let mimeparser = MimeMessage::from_bytes(&t, &raw[..], None).await.unwrap();
+    let mimeparser = MimeMessage::from_bytes(&t, &raw[..]).await.unwrap();
     assert_eq!(mimeparser.parts.len(), 1);
     assert_eq!(mimeparser.parts[0].typ, Viewtype::Text);
     assert!(mimeparser.user_avatar.unwrap().is_change());
@@ -467,9 +463,7 @@ async fn test_mimeparser_with_avatars() {
     let raw = include_bytes!("../../test-data/message/mail_with_user_and_group_avatars.eml");
     let raw = String::from_utf8_lossy(raw).to_string();
     let raw = raw.replace("Chat-User-Avatar:", "Xhat-Xser-Xvatar:");
-    let mimeparser = MimeMessage::from_bytes(&t, raw.as_bytes(), None)
-        .await
-        .unwrap();
+    let mimeparser = MimeMessage::from_bytes(&t, raw.as_bytes()).await.unwrap();
     assert_eq!(mimeparser.parts.len(), 1);
     assert_eq!(mimeparser.parts[0].typ, Viewtype::Image);
     assert_eq!(mimeparser.user_avatar, None);
@@ -485,7 +479,7 @@ async fn test_mimeparser_with_videochat() {
     let t = TestContext::new_alice().await;
 
     let raw = include_bytes!("../../test-data/message/videochat_invitation.eml");
-    let mimeparser = MimeMessage::from_bytes(&t, &raw[..], None).await.unwrap();
+    let mimeparser = MimeMessage::from_bytes(&t, &raw[..]).await.unwrap();
     assert_eq!(mimeparser.parts.len(), 1);
     assert_eq!(mimeparser.parts[0].typ, Viewtype::Text);
     assert_eq!(mimeparser.parts[0].param.get(Param::WebrtcRoom), None);
@@ -528,7 +522,7 @@ Content-Disposition: attachment; filename=\"message.kml\"\n\
 --==break==--\n\
 ;";
 
-    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(
@@ -578,7 +572,7 @@ Disposition: manual-action/MDN-sent-automatically; displayed\n\
 --kJBbU58X1xeWNHgBtTbMk80M5qnV4N--\n\
 ";
 
-    let message = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let message = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(
@@ -659,7 +653,7 @@ Disposition: manual-action/MDN-sent-automatically; displayed\n\
 --outer--\n\
 ";
 
-    let message = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let message = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(
@@ -706,7 +700,7 @@ Additional-Message-IDs: <foo@example.com> <foo@example.net>\n\
 --kJBbU58X1xeWNHgBtTbMk80M5qnV4N--\n\
 ";
 
-    let message = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let message = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(
@@ -753,7 +747,7 @@ MDYyMDYxNTE1RTlDOEE4Cj4+CnN0YXJ0eHJlZgo4Mjc4CiUlRU9GCg==
 ------=_Part_25_46172632.1581201680436--
 "#;
 
-    let message = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let message = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(
@@ -797,7 +791,7 @@ MDYyMDYxNTE1RTlDOEE4Cj4+CnN0YXJ0eHJlZgo4Mjc4CiUlRU9GCg==
 ------=_Part_25_46172632.1581201680436--
 "#;
 
-    let message = MimeMessage::from_bytes(&t, &raw[..], None).await.unwrap();
+    let message = MimeMessage::from_bytes(&t, &raw[..]).await.unwrap();
 
     assert_eq!(message.parts.len(), 1);
     assert_eq!(message.parts[0].typ, Viewtype::File);
@@ -839,7 +833,7 @@ iVBORw0KGgoAAAANSUhEUgAAACAAAAAeCAAAAABoYUP1AAAAAXNSR0IArs4c6QAAAo1JREFUKJFdkdFu
 ----11019878869865180--
 "#;
 
-    let message = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let message = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(message.get_subject(), Some("example".to_string()));
@@ -903,7 +897,7 @@ iVBORw0KGgoAAAANSUhEUgAAACAAAAAeCAAAAABoYUP1AAAAAXNSR0IArs4c6QAAAo1JREFUKJFdkdFu
 
 --------------779C1631600DF3DB8C02E53A--"#;
 
-    let message = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let message = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(message.get_subject(), Some("Test subject".to_string()));
@@ -966,7 +960,7 @@ iVBORw0KGgoAAAANSUhEUgAAACAAAAAeCAAAAABoYUP1AAAAAXNSR0IArs4c6QAAAo1JREFUKJFdkdFu
 ------=_NextPart_000_0003_01D622B3.CA753E60--
 "#;
 
-    let message = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let message = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(
@@ -1064,7 +1058,7 @@ From: alice <alice@example.org>
 Reply
 "##;
 
-    let message = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let message = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(
@@ -1096,7 +1090,7 @@ From: alice <alice@example.org>
 > Just a quote.
 "##;
 
-    let message = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let message = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(
@@ -1130,7 +1124,7 @@ On 2020-10-25, Bob wrote:
 > A quote.
 "##;
 
-    let message = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let message = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(message.get_subject(), Some("Re: top posting".to_string()));
@@ -1148,7 +1142,7 @@ On 2020-10-25, Bob wrote:
 async fn test_attachment_quote() {
     let context = TestContext::new_alice().await;
     let raw = include_bytes!("../../test-data/message/quote_attach.eml");
-    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
 
@@ -1166,7 +1160,7 @@ async fn test_attachment_quote() {
 async fn test_quote_div() {
     let t = TestContext::new_alice().await;
     let raw = include_bytes!("../../test-data/message/gmx-quote.eml");
-    let mimeparser = MimeMessage::from_bytes(&t, raw, None).await.unwrap();
+    let mimeparser = MimeMessage::from_bytes(&t, raw).await.unwrap();
     assert_eq!(mimeparser.parts[0].msg, "YIPPEEEEEE\n\nMulti-line");
     assert_eq!(mimeparser.parts[0].param.get(Param::Quote).unwrap(), "Now?");
 }
@@ -1176,7 +1170,7 @@ async fn test_allinkl_blockquote() {
     // all-inkl.com puts quotes into `<blockquote> </blockquote>`.
     let t = TestContext::new_alice().await;
     let raw = include_bytes!("../../test-data/message/allinkl-quote.eml");
-    let mimeparser = MimeMessage::from_bytes(&t, raw, None).await.unwrap();
+    let mimeparser = MimeMessage::from_bytes(&t, raw).await.unwrap();
     assert!(mimeparser.parts[0].msg.starts_with("It's 1.0."));
     assert_eq!(
         mimeparser.parts[0].param.get(Param::Quote).unwrap(),
@@ -1217,7 +1211,7 @@ async fn test_add_subj_to_multimedia_msg() {
 async fn test_mime_modified_plain() {
     let t = TestContext::new_alice().await;
     let raw = include_bytes!("../../test-data/message/text_plain_unspecified.eml");
-    let mimeparser = MimeMessage::from_bytes(&t.ctx, raw, None).await.unwrap();
+    let mimeparser = MimeMessage::from_bytes(&t.ctx, raw).await.unwrap();
     assert!(!mimeparser.is_mime_modified);
     assert_eq!(
         mimeparser.parts[0].msg,
@@ -1229,7 +1223,7 @@ async fn test_mime_modified_plain() {
 async fn test_mime_modified_alt_plain_html() {
     let t = TestContext::new_alice().await;
     let raw = include_bytes!("../../test-data/message/text_alt_plain_html.eml");
-    let mimeparser = MimeMessage::from_bytes(&t.ctx, raw, None).await.unwrap();
+    let mimeparser = MimeMessage::from_bytes(&t.ctx, raw).await.unwrap();
     assert!(mimeparser.is_mime_modified);
     assert_eq!(
         mimeparser.parts[0].msg,
@@ -1241,7 +1235,7 @@ async fn test_mime_modified_alt_plain_html() {
 async fn test_mime_modified_alt_plain() {
     let t = TestContext::new_alice().await;
     let raw = include_bytes!("../../test-data/message/text_alt_plain.eml");
-    let mimeparser = MimeMessage::from_bytes(&t.ctx, raw, None).await.unwrap();
+    let mimeparser = MimeMessage::from_bytes(&t.ctx, raw).await.unwrap();
     assert!(!mimeparser.is_mime_modified);
     assert_eq!(
         mimeparser.parts[0].msg,
@@ -1256,7 +1250,7 @@ async fn test_mime_modified_alt_plain() {
 async fn test_mime_modified_alt_html() {
     let t = TestContext::new_alice().await;
     let raw = include_bytes!("../../test-data/message/text_alt_html.eml");
-    let mimeparser = MimeMessage::from_bytes(&t.ctx, raw, None).await.unwrap();
+    let mimeparser = MimeMessage::from_bytes(&t.ctx, raw).await.unwrap();
     assert!(mimeparser.is_mime_modified);
     assert_eq!(
         mimeparser.parts[0].msg,
@@ -1268,7 +1262,7 @@ async fn test_mime_modified_alt_html() {
 async fn test_mime_modified_html() {
     let t = TestContext::new_alice().await;
     let raw = include_bytes!("../../test-data/message/text_html.eml");
-    let mimeparser = MimeMessage::from_bytes(&t.ctx, raw, None).await.unwrap();
+    let mimeparser = MimeMessage::from_bytes(&t.ctx, raw).await.unwrap();
     assert!(mimeparser.is_mime_modified);
     assert_eq!(
         mimeparser.parts[0].msg,
@@ -1288,7 +1282,7 @@ async fn test_mime_modified_large_plain() -> Result<()> {
     assert!(long_txt.len() > DC_DESIRED_TEXT_LEN);
 
     {
-        let mimemsg = MimeMessage::from_bytes(&t, long_txt.as_ref(), None).await?;
+        let mimemsg = MimeMessage::from_bytes(&t, long_txt.as_ref()).await?;
         assert!(mimemsg.is_mime_modified);
         assert!(
             mimemsg.parts[0].msg.matches("just repeated").count()
@@ -1321,7 +1315,7 @@ async fn test_mime_modified_large_plain() -> Result<()> {
 
     t.set_config(Config::Bot, Some("1")).await?;
     {
-        let mimemsg = MimeMessage::from_bytes(&t, long_txt.as_ref(), None).await?;
+        let mimemsg = MimeMessage::from_bytes(&t, long_txt.as_ref()).await?;
         assert!(!mimemsg.is_mime_modified);
         assert_eq!(
             format!("{}\n", mimemsg.parts[0].msg),
@@ -1368,7 +1362,7 @@ async fn test_x_microsoft_original_message_id() {
                 MIME-Version: 1.0\n\
                 \n\
                 Does it work with outlook now?\n\
-                ", None)
+                ")
             .await
             .unwrap();
     assert_eq!(
@@ -1418,7 +1412,7 @@ async fn test_extra_imf_headers() -> Result<()> {
             "Message-ID:",
             "Chat-Forty-Two: 42\r\nForty-Two: 42\r\nMessage-ID:",
         );
-        let msg = MimeMessage::from_bytes(t, payload.as_bytes(), None).await?;
+        let msg = MimeMessage::from_bytes(t, payload.as_bytes()).await?;
         assert!(msg.headers.contains_key("chat-version"));
         assert!(!msg.headers.contains_key("chat-forty-two"));
         assert_ne!(msg.headers.contains_key("forty-two"), std_hp_composing);
@@ -1582,7 +1576,7 @@ async fn test_ms_exchange_mdn() -> Result<()> {
     // 1. Test mimeparser directly
     let mdn =
         include_bytes!("../../test-data/message/ms_exchange_report_disposition_notification.eml");
-    let mimeparser = MimeMessage::from_bytes(&t.ctx, mdn, None).await?;
+    let mimeparser = MimeMessage::from_bytes(&t.ctx, mdn).await?;
     assert_eq!(mimeparser.mdn_reports.len(), 1);
     assert_eq!(
         mimeparser.mdn_reports[0].original_message_id.as_deref(),
@@ -1608,7 +1602,6 @@ async fn test_receive_eml() -> Result<()> {
     let mime_message = MimeMessage::from_bytes(
         &alice,
         include_bytes!("../../test-data/message/attached-eml.eml"),
-        None,
     )
     .await?;
 
@@ -1651,7 +1644,6 @@ Content-Disposition: reaction\n\
 \n\
 \u{1F44D}"
             .as_bytes(),
-        None,
     )
     .await?;
 
@@ -1673,7 +1665,7 @@ async fn test_jpeg_as_application_octet_stream() -> Result<()> {
     let context = TestContext::new_alice().await;
     let raw = include_bytes!("../../test-data/message/jpeg-as-application-octet-stream.eml");
 
-    let msg = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let msg = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(msg.parts.len(), 1);
@@ -1691,7 +1683,7 @@ async fn test_schleuder() -> Result<()> {
     let context = TestContext::new_alice().await;
     let raw = include_bytes!("../../test-data/message/schleuder.eml");
 
-    let msg = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let msg = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(msg.parts.len(), 2);
@@ -1711,7 +1703,7 @@ async fn test_tlsrpt() -> Result<()> {
     let context = TestContext::new_alice().await;
     let raw = include_bytes!("../../test-data/message/tlsrpt.eml");
 
-    let msg = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let msg = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(msg.parts.len(), 1);
@@ -1744,7 +1736,6 @@ async fn test_time_in_future() -> Result<()> {
               Content-Type: text/plain; charset=utf-8\n\
               \n\
               Hi",
-        None,
     )
     .await?;
 
@@ -1806,7 +1797,7 @@ Content-Type: text/plain; charset=utf-8
 /help
 "#;
 
-    let message = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let message = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(message.get_subject(), Some("Some subject".to_string()));
@@ -1847,7 +1838,7 @@ async fn test_take_last_header() {
                     Hello\n\
                     ";
 
-    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..], None)
+    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..])
         .await
         .unwrap();
     assert_eq!(
@@ -1900,9 +1891,7 @@ It DOES end with a linebreak.\r
 \r
 This is the epilogue.  It is also to be ignored.";
 
-    let mimeparser = MimeMessage::from_bytes(&context, &raw[..], None)
-        .await
-        .unwrap();
+    let mimeparser = MimeMessage::from_bytes(&context, &raw[..]).await.unwrap();
 
     assert_eq!(mimeparser.parts.len(), 2);
 
@@ -1948,7 +1937,7 @@ Message with a correct Message-ID hidden header
 --luTiGu6GBoVLCvTkzVtmZmwsmhkNMw--
 "#;
 
-    let message = MimeMessage::from_bytes(t, &raw[..], None).await.unwrap();
+    let message = MimeMessage::from_bytes(t, &raw[..]).await.unwrap();
     assert_eq!(message.get_rfc724_mid().unwrap(), "foo@example.org");
 }
 
@@ -2126,9 +2115,7 @@ Third alternative.
 --boundary--
 "#;
 
-    let message = MimeMessage::from_bytes(context, &raw[..], None)
-        .await
-        .unwrap();
+    let message = MimeMessage::from_bytes(context, &raw[..]).await.unwrap();
     assert_eq!(message.parts.len(), 1);
     assert_eq!(message.parts[0].typ, Viewtype::Text);
     assert_eq!(message.parts[0].msg, "Third alternative.");

src/param.rs

@@ -251,6 +251,13 @@ pub enum Param {
 
     /// For info messages: Contact ID in added or removed to a group.
     ContactAddedRemoved = b'5',
+
+    /// For (pre-)Message: ViewType of the Post-Message,
+    /// because pre message is always `Viewtype::Text`.
+    PostMessageViewtype = b'8',
+
+    /// For (pre-)Message: File byte size of Post-Message attachment
+    PostMessageFileBytes = b'9',
 }
 
 /// An object for handling key=value parameter lists.
@@ -441,6 +448,15 @@ impl Params {
         }
         self
     }
+
+    /// Merge in parameters from other Params struct,
+    /// overwriting the keys that are in both
+    /// with the values from the new Params struct.
+    pub fn merge_in_from_params(&mut self, new_params: Self) -> &mut Self {
+        let mut new_params = new_params;
+        self.inner.append(&mut new_params.inner);
+        self
+    }
 }
 
 #[cfg(test)]
@@ -503,4 +519,18 @@ mod tests {
         assert_eq!(p.get(Param::Height), Some("14"));
         Ok(())
     }
+
+    #[test]
+    fn test_merge() -> Result<()> {
+        let mut p = Params::from_str("w=12\na=5\nh=14")?;
+        let p2 = Params::from_str("L=1\nh=17")?;
+        assert_eq!(p.len(), 3);
+        p.merge_in_from_params(p2);
+        assert_eq!(p.len(), 4);
+        assert_eq!(p.get(Param::Width), Some("12"));
+        assert_eq!(p.get(Param::Height), Some("17"));
+        assert_eq!(p.get(Param::Forwarded), Some("5"));
+        assert_eq!(p.get(Param::IsEdited), Some("1"));
+        Ok(())
+    }
 }

src/reaction.rs

@@ -392,9 +392,8 @@ mod tests {
     use crate::chatlist::Chatlist;
     use crate::config::Config;
     use crate::contact::{Contact, Origin};
-    use crate::download::DownloadState;
     use crate::message::{MessageState, Viewtype, delete_msgs};
-    use crate::receive_imf::{receive_imf, receive_imf_from_inbox};
+    use crate::receive_imf::receive_imf;
     use crate::sql::housekeeping;
     use crate::test_utils::E2EE_INFO_MSGS;
     use crate::test_utils::TestContext;
@@ -924,73 +923,6 @@ Content-Disposition: reaction\n\
         Ok(())
     }
 
-    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-    async fn test_partial_download_and_reaction() -> Result<()> {
-        let alice = TestContext::new_alice().await;
-        let bob = TestContext::new_bob().await;
-
-        alice
-            .create_chat_with_contact("Bob", "bob@example.net")
-            .await;
-
-        let msg_header = "From: Bob <bob@example.net>\n\
-                    To: Alice <alice@example.org>\n\
-                    Chat-Version: 1.0\n\
-                    Subject: subject\n\
-                    Message-ID: <first@example.org>\n\
-                    Date: Sun, 14 Nov 2021 00:10:00 +0000\
-                    Content-Type: text/plain";
-        let msg_full = format!("{msg_header}\n\n100k text...");
-
-        // Alice downloads message from Bob partially.
-        let alice_received_message = receive_imf_from_inbox(
-            &alice,
-            "first@example.org",
-            msg_header.as_bytes(),
-            false,
-            Some(100000),
-        )
-        .await?
-        .unwrap();
-        let alice_msg_id = *alice_received_message.msg_ids.first().unwrap();
-
-        // Bob downloads own message on the other device.
-        let bob_received_message = receive_imf(&bob, msg_full.as_bytes(), false)
-            .await?
-            .unwrap();
-        let bob_msg_id = *bob_received_message.msg_ids.first().unwrap();
-
-        // Bob reacts to own message.
-        send_reaction(&bob, bob_msg_id, "👍").await.unwrap();
-        let bob_reaction_msg = bob.pop_sent_msg().await;
-
-        // Alice receives a reaction.
-        alice.recv_msg_hidden(&bob_reaction_msg).await;
-
-        let reactions = get_msg_reactions(&alice, alice_msg_id).await?;
-        assert_eq!(reactions.to_string(), "👍1");
-        let msg = Message::load_from_db(&alice, alice_msg_id).await?;
-        assert_eq!(msg.download_state(), DownloadState::Available);
-
-        // Alice downloads full message.
-        receive_imf_from_inbox(
-            &alice,
-            "first@example.org",
-            msg_full.as_bytes(),
-            false,
-            None,
-        )
-        .await?;
-
-        // Check that reaction is still on the message after full download.
-        let msg = Message::load_from_db(&alice, alice_msg_id).await?;
-        assert_eq!(msg.download_state(), DownloadState::Done);
-        let reactions = get_msg_reactions(&alice, alice_msg_id).await?;
-        assert_eq!(reactions.to_string(), "👍1");
-
-        Ok(())
-    }
-
     #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
     async fn test_send_reaction_multidevice() -> Result<()> {
         let mut tcm = TestContextManager::new();

src/receive_imf.rs

@@ -20,16 +20,14 @@ use crate::constants::{self, Blocked, Chattype, DC_CHAT_ID_TRASH, EDITED_PREFIX,
 use crate::contact::{self, Contact, ContactId, Origin, mark_contact_id_as_verified};
 use crate::context::Context;
 use crate::debug_logging::maybe_set_logging_xdc_inner;
-use crate::download::DownloadState;
+use crate::download::{DownloadState, premessage_is_downloaded_for};
 use crate::ephemeral::{Timer as EphemeralTimer, stock_ephemeral_timer_changed};
 use crate::events::EventType;
 use crate::headerdef::{HeaderDef, HeaderDefMap};
 use crate::imap::{GENERATED_PREFIX, markseen_on_imap_table};
 use crate::key::{DcKey, Fingerprint};
 use crate::key::{self_fingerprint, self_fingerprint_opt};
-use crate::log::LogExt;
-use crate::log::warn;
-use crate::logged_debug_assert;
+use crate::log::{LogExt as _, warn};
 use crate::message::{
     self, Message, MessageState, MessengerMessage, MsgId, Viewtype, rfc724_mid_exists,
 };
@@ -47,6 +45,7 @@ use crate::tools::{
     self, buf_compress, normalize_text, remove_subject_prefix, validate_broadcast_secret,
 };
 use crate::{chatlist_events, ensure_and_debug_assert, ensure_and_debug_assert_eq, location};
+use crate::{logged_debug_assert, mimeparser};
 
 /// This is the struct that is returned after receiving one email (aka MIME message).
 ///
@@ -157,24 +156,7 @@ pub async fn receive_imf(
     let mail = mailparse::parse_mail(imf_raw).context("can't parse mail")?;
     let rfc724_mid = crate::imap::prefetch_get_message_id(&mail.headers)
         .unwrap_or_else(crate::imap::create_message_id);
-    if let Some(download_limit) = context.download_limit().await? {
-        let download_limit: usize = download_limit.try_into()?;
-        if imf_raw.len() > download_limit {
-            let head = std::str::from_utf8(imf_raw)?
-                .split("\r\n\r\n")
-                .next()
-                .context("No empty line in the message")?;
-            return receive_imf_from_inbox(
-                context,
-                &rfc724_mid,
-                head.as_bytes(),
-                seen,
-                Some(imf_raw.len().try_into()?),
-            )
-            .await;
-        }
-    }
-    receive_imf_from_inbox(context, &rfc724_mid, imf_raw, seen, None).await
+    receive_imf_from_inbox(context, &rfc724_mid, imf_raw, seen).await
 }
 
 /// Emulates reception of a message from "INBOX".
@@ -186,9 +168,8 @@ pub(crate) async fn receive_imf_from_inbox(
     rfc724_mid: &str,
     imf_raw: &[u8],
     seen: bool,
-    is_partial_download: Option<u32>,
 ) -> Result<Option<ReceivedMsg>> {
-    receive_imf_inner(context, rfc724_mid, imf_raw, seen, is_partial_download).await
+    receive_imf_inner(context, rfc724_mid, imf_raw, seen).await
 }
 
 /// Inserts a tombstone into `msgs` table
@@ -211,7 +192,6 @@ async fn get_to_and_past_contact_ids(
     context: &Context,
     mime_parser: &MimeMessage,
     chat_assignment: &ChatAssignment,
-    is_partial_download: Option<u32>,
     parent_message: &Option<Message>,
     incoming_origin: Origin,
 ) -> Result<(Vec<Option<ContactId>>, Vec<Option<ContactId>>)> {
@@ -254,7 +234,7 @@ async fn get_to_and_past_contact_ids(
         ChatAssignment::ExistingChat { chat_id, .. } => Some(*chat_id),
         ChatAssignment::MailingListOrBroadcast => None,
         ChatAssignment::OneOneChat => {
-            if is_partial_download.is_none() && !mime_parser.incoming {
+            if !mime_parser.incoming {
                 parent_message.as_ref().map(|m| m.chat_id)
             } else {
                 None
@@ -484,15 +464,17 @@ async fn get_to_and_past_contact_ids(
 /// downloaded again, sets `chat_id=DC_CHAT_ID_TRASH` and returns `Ok(Some(…))`.
 /// If the message is so wrong that we didn't even create a database entry,
 /// returns `Ok(None)`.
-///
-/// If `is_partial_download` is set, it contains the full message size in bytes.
 pub(crate) async fn receive_imf_inner(
     context: &Context,
     rfc724_mid: &str,
     imf_raw: &[u8],
     seen: bool,
-    is_partial_download: Option<u32>,
 ) -> Result<Option<ReceivedMsg>> {
+    ensure!(
+        !context
+            .get_config_bool(Config::SimulateReceiveImfError)
+            .await?
+    );
     if std::env::var(crate::DCC_MIME_DEBUG).is_ok() {
         info!(
             context,
@@ -500,16 +482,8 @@ pub(crate) async fn receive_imf_inner(
             String::from_utf8_lossy(imf_raw),
         );
     }
-    if is_partial_download.is_none() {
-        ensure!(
-            !context
-                .get_config_bool(Config::FailOnReceivingFullMsg)
-                .await?
-        );
-    }
 
-    let mut mime_parser = match MimeMessage::from_bytes(context, imf_raw, is_partial_download).await
-    {
+    let mut mime_parser = match MimeMessage::from_bytes(context, imf_raw).await {
         Err(err) => {
             warn!(context, "receive_imf: can't parse MIME: {err:#}.");
             if rfc724_mid.starts_with(GENERATED_PREFIX) {
@@ -542,7 +516,15 @@ pub(crate) async fn receive_imf_inner(
     // check, if the mail is already in our database.
     // make sure, this check is done eg. before securejoin-processing.
     let (replace_msg_id, replace_chat_id);
-    if let Some(old_msg_id) = message::rfc724_mid_exists(context, rfc724_mid).await? {
+    if mime_parser.pre_message == Some(mimeparser::PreMessageMode::PostMessage) {
+        // Post-Message just replace the attachment and mofified Params, not the whole message
+        // This is done in the `handle_post_message` method.
+        replace_msg_id = None;
+        replace_chat_id = None;
+    } else if let Some(old_msg_id) = message::rfc724_mid_exists(context, rfc724_mid).await? {
+        // This code handles the download of old partial download stub messages
+        // It will be removed after a transitioning period,
+        // after we have released a few versions with pre-messages
         replace_msg_id = Some(old_msg_id);
         replace_chat_id = if let Some(msg) = Message::load_from_db_optional(context, old_msg_id)
             .await?
@@ -615,11 +597,7 @@ pub(crate) async fn receive_imf_inner(
         &mime_parser.from,
         fingerprint,
         prevent_rename,
-        is_partial_download.is_some()
-            && mime_parser
-                .get_header(HeaderDef::ContentType)
-                .unwrap_or_default()
-                .starts_with("multipart/encrypted"),
+        false,
     )
     .await?
     {
@@ -651,22 +629,14 @@ pub(crate) async fn receive_imf_inner(
     .await?
     .filter(|p| Some(p.id) != replace_msg_id);
 
-    let chat_assignment = decide_chat_assignment(
-        context,
-        &mime_parser,
-        &parent_message,
-        rfc724_mid,
-        from_id,
-        &is_partial_download,
-    )
-    .await?;
+    let chat_assignment =
+        decide_chat_assignment(context, &mime_parser, &parent_message, rfc724_mid, from_id).await?;
     info!(context, "Chat assignment is {chat_assignment:?}.");
 
     let (to_ids, past_ids) = get_to_and_past_contact_ids(
         context,
         &mime_parser,
         &chat_assignment,
-        is_partial_download,
         &parent_message,
         incoming_origin,
     )
@@ -763,7 +733,6 @@ pub(crate) async fn receive_imf_inner(
             to_id,
             allow_creation,
             &mut mime_parser,
-            is_partial_download,
             parent_message,
         )
         .await?;
@@ -779,7 +748,6 @@ pub(crate) async fn receive_imf_inner(
             rfc724_mid_orig,
             from_id,
             seen,
-            is_partial_download,
             replace_msg_id,
             prevent_rename,
             chat_id,
@@ -947,9 +915,7 @@ pub(crate) async fn receive_imf_inner(
     let delete_server_after = context.get_config_delete_server_after().await?;
 
     if !received_msg.msg_ids.is_empty() {
-        let target = if received_msg.needs_delete_job
-            || (delete_server_after == Some(0) && is_partial_download.is_none())
-        {
+        let target = if received_msg.needs_delete_job || delete_server_after == Some(0) {
             Some(context.get_delete_msgs_target().await?)
         } else {
             None
@@ -978,7 +944,7 @@ pub(crate) async fn receive_imf_inner(
         }
     }
 
-    if is_partial_download.is_none() && mime_parser.is_call() {
+    if mime_parser.is_call() {
         context
             .handle_call_msg(insert_msg_id, &mime_parser, from_id)
             .await?;
@@ -1027,7 +993,7 @@ pub(crate) async fn receive_imf_inner(
 /// * `find_key_contact_by_addr`: if true, we only know the e-mail address
 ///   of the contact, but not the fingerprint,
 ///   yet want to assign the message to some key-contact.
-///   This can happen during prefetch or when the message is partially downloaded.
+///   This can happen during prefetch.
 ///   If we get it wrong, the message will be placed into the correct
 ///   chat after downloading.
 ///
@@ -1121,7 +1087,6 @@ async fn decide_chat_assignment(
     parent_message: &Option<Message>,
     rfc724_mid: &str,
     from_id: ContactId,
-    is_partial_download: &Option<u32>,
 ) -> Result<ChatAssignment> {
     let should_trash = if !mime_parser.mdn_reports.is_empty() {
         info!(context, "Message is an MDN (TRASH).");
@@ -1137,9 +1102,40 @@ async fn decide_chat_assignment(
     {
         info!(context, "Chat edit/delete/iroh/sync message (TRASH).");
         true
-    } else if is_partial_download.is_none()
-        && (mime_parser.is_system_message == SystemMessage::CallAccepted
-            || mime_parser.is_system_message == SystemMessage::CallEnded)
+    } else if let Some(pre_message) = &mime_parser.pre_message {
+        use crate::mimeparser::PreMessageMode::*;
+        match pre_message {
+            PostMessage => {
+                // if pre message exist, then trash after replacing, otherwise treat as normal message
+                let pre_message_exists = premessage_is_downloaded_for(context, rfc724_mid).await?;
+                info!(
+                    context,
+                    "Message is a Post-Message ({}).",
+                    if pre_message_exists {
+                        "pre-message exists already, so trash after replacing attachment"
+                    } else {
+                        "no pre-message -> Keep"
+                    }
+                );
+                pre_message_exists
+            }
+            PreMessage {
+                post_msg_rfc724_mid,
+                ..
+            } => {
+                // if post message already exists, then trash/ignore
+                let post_msg_exists =
+                    premessage_is_downloaded_for(context, post_msg_rfc724_mid).await?;
+                info!(
+                    context,
+                    "Message is a Pre-Message (post_msg_exists:{post_msg_exists})."
+                );
+                post_msg_exists
+                // TODO find out if trashing affects multi device usage?
+            }
+        }
+    } else if mime_parser.is_system_message == SystemMessage::CallAccepted
+        || mime_parser.is_system_message == SystemMessage::CallEnded
     {
         info!(context, "Call state changed (TRASH).");
         true
@@ -1240,7 +1236,7 @@ async fn decide_chat_assignment(
             }
         } else if let Some(parent) = &parent_message {
             if let Some((chat_id, chat_id_blocked)) =
-                lookup_chat_by_reply(context, mime_parser, parent, is_partial_download).await?
+                lookup_chat_by_reply(context, mime_parser, parent).await?
             {
                 // Try to assign to a chat based on In-Reply-To/References.
                 ChatAssignment::ExistingChat {
@@ -1262,7 +1258,7 @@ async fn decide_chat_assignment(
         }
     } else if let Some(parent) = &parent_message {
         if let Some((chat_id, chat_id_blocked)) =
-            lookup_chat_by_reply(context, mime_parser, parent, is_partial_download).await?
+            lookup_chat_by_reply(context, mime_parser, parent).await?
         {
             // Try to assign to a chat based on In-Reply-To/References.
             ChatAssignment::ExistingChat {
@@ -1304,7 +1300,6 @@ async fn do_chat_assignment(
     to_id: ContactId,
     allow_creation: bool,
     mime_parser: &mut MimeMessage,
-    is_partial_download: Option<u32>,
     parent_message: Option<Message>,
 ) -> Result<(ChatId, Blocked, bool)> {
     let is_bot = context.get_config_bool(Config::Bot).await?;
@@ -1355,7 +1350,6 @@ async fn do_chat_assignment(
                     && let Some((new_chat_id, new_chat_id_blocked)) = create_group(
                         context,
                         mime_parser,
-                        is_partial_download.is_some(),
                         create_blocked,
                         from_id,
                         to_ids,
@@ -1404,7 +1398,6 @@ async fn do_chat_assignment(
                         to_ids,
                         allow_creation || test_normal_chat.is_some(),
                         create_blocked,
-                        is_partial_download.is_some(),
                     )
                     .await?
                 {
@@ -1486,7 +1479,6 @@ async fn do_chat_assignment(
                     && let Some((new_chat_id, new_chat_id_blocked)) = create_group(
                         context,
                         mime_parser,
-                        is_partial_download.is_some(),
                         Blocked::Not,
                         from_id,
                         to_ids,
@@ -1550,7 +1542,6 @@ async fn do_chat_assignment(
                         to_ids,
                         allow_creation,
                         Blocked::Not,
-                        is_partial_download.is_some(),
                     )
                     .await?
                 {
@@ -1631,7 +1622,6 @@ async fn add_parts(
     rfc724_mid: &str,
     from_id: ContactId,
     seen: bool,
-    is_partial_download: Option<u32>,
     mut replace_msg_id: Option<MsgId>,
     prevent_rename: bool,
     mut chat_id: ChatId,
@@ -1703,10 +1693,9 @@ async fn add_parts(
         .get_rfc724_mid()
         .unwrap_or(rfc724_mid.to_string());
 
-    // Extract ephemeral timer from the message or use the existing timer if the message is not fully downloaded.
-    let mut ephemeral_timer = if is_partial_download.is_some() {
-        chat_id.get_ephemeral_timer(context).await?
-    } else if let Some(value) = mime_parser.get_header(HeaderDef::EphemeralTimer) {
+    // Extract ephemeral timer from the message
+    let mut ephemeral_timer = if let Some(value) = mime_parser.get_header(HeaderDef::EphemeralTimer)
+    {
         match value.parse::<EphemeralTimer>() {
             Ok(timer) => timer,
             Err(err) => {
@@ -1909,7 +1898,6 @@ async fn add_parts(
     let chat_id = if better_msg
         .as_ref()
         .is_some_and(|better_msg| better_msg.is_empty())
-        && is_partial_download.is_none()
     {
         DC_CHAT_ID_TRASH
     } else {
@@ -1958,10 +1946,10 @@ async fn add_parts(
     }
 
     handle_edit_delete(context, mime_parser, from_id).await?;
+    handle_post_message(context, mime_parser, from_id).await?;
 
-    if is_partial_download.is_none()
-        && (mime_parser.is_system_message == SystemMessage::CallAccepted
-            || mime_parser.is_system_message == SystemMessage::CallEnded)
+    if mime_parser.is_system_message == SystemMessage::CallAccepted
+        || mime_parser.is_system_message == SystemMessage::CallEnded
     {
         if let Some(field) = mime_parser.get_header(HeaderDef::InReplyTo) {
             if let Some(call) =
@@ -2042,6 +2030,14 @@ async fn add_parts(
             }
         };
 
+        if let Some(mimeparser::PreMessageMode::PreMessage {
+            metadata: Some(metadata),
+            ..
+        }) = &mime_parser.pre_message
+        {
+            param.apply_from_pre_msg_metadata(metadata);
+        };
+
         // If you change which information is skipped if the message is trashed,
         // also change `MsgId::trash()` and `delete_expired_messages()`
         let trash = chat_id.is_trash() || (is_location_kml && part_is_empty && !save_mime_modified);
@@ -2085,14 +2081,20 @@ RETURNING id
 "#)?;
                 let row_id: MsgId = stmt.query_row(params![
                     replace_msg_id,
-                    rfc724_mid_orig,
+                    if let Some(mimeparser::PreMessageMode::PreMessage {post_msg_rfc724_mid, .. }) = &mime_parser.pre_message {
+                        post_msg_rfc724_mid
+                    } else { rfc724_mid_orig },
                     if trash { DC_CHAT_ID_TRASH } else { chat_id },
                     if trash { ContactId::UNDEFINED } else { from_id },
                     if trash { ContactId::UNDEFINED } else { to_id },
                     sort_timestamp,
                     if trash { 0 } else { mime_parser.timestamp_sent },
                     if trash { 0 } else { mime_parser.timestamp_rcvd },
-                    if trash { Viewtype::Unknown } else { typ },
+                    if trash {
+                        Viewtype::Unknown
+                    } else if let Some(mimeparser::PreMessageMode::PreMessage {..}) = mime_parser.pre_message {
+                        Viewtype::Text
+                    } else { typ },
                     if trash { MessageState::Undefined } else { state },
                     if trash { MessengerMessage::No } else { is_dc_message },
                     if trash || hidden { "" } else { msg },
@@ -2104,7 +2106,11 @@ RETURNING id
                         param.to_string()
                     },
                     !trash && hidden,
-                    if trash { 0 } else { part.bytes as isize },
+                    if trash {
+                        0
+                    } else {
+                        part.bytes as isize
+                    },
                     if save_mime_modified && !(trash || hidden) {
                         mime_headers.clone()
                     } else {
@@ -2118,10 +2124,10 @@ RETURNING id
                     if trash { 0 } else { ephemeral_timestamp },
                     if trash {
                         DownloadState::Done
-                    } else if is_partial_download.is_some() {
-                        DownloadState::Available
                     } else if mime_parser.decrypting_failed {
                         DownloadState::Undecipherable
+                    } else if let Some(mimeparser::PreMessageMode::PreMessage {..}) = mime_parser.pre_message {
+                        DownloadState::Available
                     } else {
                         DownloadState::Done
                     },
@@ -2314,6 +2320,82 @@ async fn handle_edit_delete(
     Ok(())
 }
 
+async fn handle_post_message(
+    context: &Context,
+    mime_parser: &MimeMessage,
+    from_id: ContactId,
+) -> Result<()> {
+    if let Some(mimeparser::PreMessageMode::PostMessage) = &mime_parser.pre_message {
+        // if Pre-Message exist, replace attachment
+        // only replacing attachment ensures that doesn't overwrite the text if it was edited before.
+        let rfc724_mid = mime_parser
+            .get_rfc724_mid()
+            .context("expected Post-Message to have a message id")?;
+
+        let Some(msg_id) = message::rfc724_mid_exists(context, &rfc724_mid).await? else {
+            warn!(
+                context,
+                "Download Post-Message: Database entry does not exist."
+            );
+            return Ok(());
+        };
+        let Some(original_msg) = Message::load_from_db_optional(context, msg_id).await? else {
+            // else: message is processed like a normal message
+            warn!(
+                context,
+                "Download Post-Message: pre message was not downloaded, yet so treat as normal message"
+            );
+            return Ok(());
+        };
+
+        if original_msg.from_id != from_id {
+            warn!(context, "Download Post-Message: Bad sender.");
+            return Ok(());
+        }
+        if let Some(part) = mime_parser.parts.first() {
+            if !part.typ.has_file() {
+                warn!(
+                    context,
+                    "Download Post-Message: First mime part's message-viewtype has no file"
+                );
+                return Ok(());
+            }
+
+            let edit_msg_showpadlock = part
+                .param
+                .get_bool(Param::GuaranteeE2ee)
+                .unwrap_or_default();
+
+            if edit_msg_showpadlock || !original_msg.get_showpadlock() {
+                let mut new_params = original_msg.param.clone();
+                new_params
+                    .merge_in_from_params(part.param.clone())
+                    .remove(Param::PostMessageFileBytes)
+                    .remove(Param::PostMessageViewtype);
+                context
+                        .sql
+                        .execute(
+                            "UPDATE msgs SET param=?, type=?, bytes=?, error=?, download_state=? WHERE id=?",
+                            (
+                                new_params.to_string(),
+                                part.typ,
+                                part.bytes as isize,
+                                part.error.as_deref().unwrap_or_default(),
+                                DownloadState::Done as u32,
+                                original_msg.id,
+                            ),
+                        )
+                        .await?;
+                context.emit_msgs_changed(original_msg.chat_id, original_msg.id);
+            } else {
+                warn!(context, "Download Post-Message: Not encrypted.");
+            }
+        }
+    }
+
+    Ok(())
+}
+
 async fn tweak_sort_timestamp(
     context: &Context,
     mime_parser: &mut MimeMessage,
@@ -2403,7 +2485,6 @@ async fn lookup_chat_by_reply(
     context: &Context,
     mime_parser: &MimeMessage,
     parent: &Message,
-    is_partial_download: &Option<u32>,
 ) -> Result<Option<(ChatId, Blocked)>> {
     // If the message is encrypted and has group ID,
     // lookup by reply should never be needed
@@ -2435,10 +2516,7 @@ async fn lookup_chat_by_reply(
     }
 
     // Do not assign unencrypted messages to encrypted chats.
-    if is_partial_download.is_none()
-        && parent_chat.is_encrypted(context).await?
-        && !mime_parser.was_encrypted()
-    {
+    if parent_chat.is_encrypted(context).await? && !mime_parser.was_encrypted() {
         return Ok(None);
     }
 
@@ -2455,18 +2533,7 @@ async fn lookup_or_create_adhoc_group(
     to_ids: &[Option<ContactId>],
     allow_creation: bool,
     create_blocked: Blocked,
-    is_partial_download: bool,
 ) -> Result<Option<(ChatId, Blocked, bool)>> {
-    // Partial download may be an encrypted message with protected Subject header. We do not want to
-    // create a group with "..." or "Encrypted message" as a subject. The same is for undecipherable
-    // messages. Instead, assign the message to 1:1 chat with the sender.
-    if is_partial_download {
-        info!(
-            context,
-            "Ad-hoc group cannot be created from partial download."
-        );
-        return Ok(None);
-    }
     if mime_parser.decrypting_failed {
         warn!(
             context,
@@ -2602,11 +2669,9 @@ async fn is_probably_private_reply(
 /// than two members, a new ad hoc group is created.
 ///
 /// On success the function returns the created (chat_id, chat_blocked) tuple.
-#[expect(clippy::too_many_arguments)]
 async fn create_group(
     context: &Context,
     mime_parser: &mut MimeMessage,
-    is_partial_download: bool,
     create_blocked: Blocked,
     from_id: ContactId,
     to_ids: &[Option<ContactId>],
@@ -2688,7 +2753,7 @@ async fn create_group(
 
     if let Some(chat_id) = chat_id {
         Ok(Some((chat_id, chat_id_blocked)))
-    } else if is_partial_download || mime_parser.decrypting_failed {
+    } else if mime_parser.decrypting_failed {
         // It is possible that the message was sent to a valid,
         // yet unknown group, which was rejected because
         // Chat-Group-Name, which is in the encrypted part, was

src/receive_imf/receive_imf_tests.rs

@@ -10,7 +10,6 @@ use crate::chat::{
 use crate::chatlist::Chatlist;
 use crate::constants::DC_GCL_FOR_FORWARDING;
 use crate::contact;
-use crate::download::MIN_DOWNLOAD_LIMIT;
 use crate::imap::prefetch_should_download;
 use crate::imex::{ImexMode, imex};
 use crate::securejoin::get_securejoin_qr;
@@ -19,8 +18,6 @@ use crate::test_utils::{
 };
 use crate::tools::{SystemTime, time};
 
-use rand::distr::SampleString;
-
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_outgoing() -> Result<()> {
     let context = TestContext::new_alice().await;
@@ -28,7 +25,7 @@ async fn test_outgoing() -> Result<()> {
                 From: alice@example.org\n\
                 \n\
                 hello";
-    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..], None).await?;
+    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..]).await?;
     assert_eq!(mimeparser.incoming, false);
     Ok(())
 }
@@ -43,7 +40,7 @@ async fn test_bad_from() {
                     References: <Gr.HcxyMARjyJy.9-uvzWPTLtV@nauta.cu>\n\
                     \n\
                     hello\x00";
-    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..], None).await;
+    let mimeparser = MimeMessage::from_bytes(&context.ctx, &raw[..]).await;
     assert!(mimeparser.is_err());
 }
 
@@ -2842,7 +2839,7 @@ References: <second@example.net> <nonexistent@example.net> <first@example.net>
 Content-Type: text/plain; charset=utf-8; format=flowed; delsp=no
 
 Message with references."#;
-    let mime_parser = MimeMessage::from_bytes(&t, &mime[..], None).await?;
+    let mime_parser = MimeMessage::from_bytes(&t, &mime[..]).await?;
 
     let parent = get_parent_message(&t, &mime_parser).await?.unwrap();
     assert_eq!(parent.id, first.id);
@@ -4385,37 +4382,6 @@ async fn test_adhoc_grp_name_no_prefix() -> Result<()> {
     Ok(())
 }
 
-#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn test_download_later() -> Result<()> {
-    let mut tcm = TestContextManager::new();
-    let alice = tcm.alice().await;
-    alice.set_config(Config::DownloadLimit, Some("1")).await?;
-    assert_eq!(alice.download_limit().await?, Some(MIN_DOWNLOAD_LIMIT));
-
-    let bob = tcm.bob().await;
-    let bob_chat = bob.create_chat(&alice).await;
-
-    // Generate a random string so OpenPGP does not compress it.
-    let text =
-        rand::distr::Alphanumeric.sample_string(&mut rand::rng(), MIN_DOWNLOAD_LIMIT as usize);
-
-    let sent_msg = bob.send_text(bob_chat.id, &text).await;
-    let msg = alice.recv_msg(&sent_msg).await;
-    assert_eq!(msg.download_state, DownloadState::Available);
-    assert_eq!(msg.state, MessageState::InFresh);
-
-    let hi_msg = tcm.send_recv(&bob, &alice, "hi").await;
-
-    alice.set_config(Config::DownloadLimit, None).await?;
-    let msg = alice.recv_msg(&sent_msg).await;
-    assert_eq!(msg.download_state, DownloadState::Done);
-    assert_eq!(msg.state, MessageState::InFresh);
-    assert_eq!(alice.get_last_msg_in(msg.chat_id).await.id, hi_msg.id);
-    assert!(msg.timestamp_sort <= hi_msg.timestamp_sort);
-
-    Ok(())
-}
-
 /// Malice can pretend they have the same address as Alice and sends a message encrypted to Alice's
 /// key but signed with another one. Alice must detect that this message is wrongly signed and not
 /// treat it as Autocrypt-encrypted.
@@ -4450,162 +4416,6 @@ async fn test_outgoing_msg_forgery() -> Result<()> {
     Ok(())
 }
 
-#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn test_create_group_with_big_msg() -> Result<()> {
-    let mut tcm = TestContextManager::new();
-    let alice = tcm.alice().await;
-    let bob = tcm.bob().await;
-    let ba_contact = bob.add_or_lookup_contact_id(&alice).await;
-    let ab_chat_id = alice.create_chat(&bob).await.id;
-
-    let file_bytes = include_bytes!("../../test-data/image/screenshot.png");
-
-    let bob_grp_id = create_group(&bob, "Group").await?;
-    add_contact_to_chat(&bob, bob_grp_id, ba_contact).await?;
-    let mut msg = Message::new(Viewtype::Image);
-    msg.set_file_from_bytes(&bob, "a.jpg", file_bytes, None)?;
-    let sent_msg = bob.send_msg(bob_grp_id, &mut msg).await;
-    assert!(msg.get_showpadlock());
-
-    alice.set_config(Config::DownloadLimit, Some("1")).await?;
-    assert_eq!(alice.download_limit().await?, Some(MIN_DOWNLOAD_LIMIT));
-    let msg = alice.recv_msg(&sent_msg).await;
-    assert_eq!(msg.download_state, DownloadState::Available);
-    let alice_chat = Chat::load_from_db(&alice, msg.chat_id).await?;
-    // Incomplete message is assigned to 1:1 chat.
-    assert_eq!(alice_chat.typ, Chattype::Single);
-
-    alice.set_config(Config::DownloadLimit, None).await?;
-    let msg = alice.recv_msg(&sent_msg).await;
-    assert_eq!(msg.download_state, DownloadState::Done);
-    assert_eq!(msg.state, MessageState::InFresh);
-    assert_eq!(msg.viewtype, Viewtype::Image);
-    assert_ne!(msg.chat_id, alice_chat.id);
-    let alice_grp = Chat::load_from_db(&alice, msg.chat_id).await?;
-    assert_eq!(alice_grp.typ, Chattype::Group);
-    assert_eq!(alice_grp.name, "Group");
-    assert_eq!(
-        chat::get_chat_contacts(&alice, alice_grp.id).await?.len(),
-        2
-    );
-
-    // Now Bob can send encrypted messages to Alice.
-
-    let bob_grp_id = create_group(&bob, "Group1").await?;
-    add_contact_to_chat(&bob, bob_grp_id, ba_contact).await?;
-    let mut msg = Message::new(Viewtype::Image);
-    msg.set_file_from_bytes(&bob, "a.jpg", file_bytes, None)?;
-    let sent_msg = bob.send_msg(bob_grp_id, &mut msg).await;
-    assert!(msg.get_showpadlock());
-
-    alice.set_config(Config::DownloadLimit, Some("1")).await?;
-    let msg = alice.recv_msg(&sent_msg).await;
-    assert_eq!(msg.download_state, DownloadState::Available);
-    // Until fully downloaded, an encrypted message must sit in the 1:1 chat.
-    assert_eq!(msg.chat_id, ab_chat_id);
-
-    alice.set_config(Config::DownloadLimit, None).await?;
-    let msg = alice.recv_msg(&sent_msg).await;
-    assert_eq!(msg.download_state, DownloadState::Done);
-    assert_eq!(msg.state, MessageState::InFresh);
-    assert_eq!(msg.viewtype, Viewtype::Image);
-    assert_ne!(msg.chat_id, ab_chat_id);
-    let alice_grp = Chat::load_from_db(&alice, msg.chat_id).await?;
-    assert_eq!(alice_grp.typ, Chattype::Group);
-    assert_eq!(alice_grp.name, "Group1");
-    assert_eq!(
-        chat::get_chat_contacts(&alice, alice_grp.id).await?.len(),
-        2
-    );
-
-    // The big message must go away from the 1:1 chat.
-    let msgs = chat::get_chat_msgs(&alice, ab_chat_id).await?;
-    assert_eq!(msgs.len(), E2EE_INFO_MSGS);
-
-    Ok(())
-}
-
-#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn test_partial_group_consistency() -> Result<()> {
-    let mut tcm = TestContextManager::new();
-    let alice = tcm.alice().await;
-    let bob = tcm.bob().await;
-    let fiona = tcm.fiona().await;
-    let bob_id = alice.add_or_lookup_contact_id(&bob).await;
-    let alice_chat_id = create_group(&alice, "foos").await?;
-    add_contact_to_chat(&alice, alice_chat_id, bob_id).await?;
-
-    send_text_msg(&alice, alice_chat_id, "populate".to_string()).await?;
-    let add = alice.pop_sent_msg().await;
-    bob.recv_msg(&add).await;
-    let bob_chat_id = bob.get_last_msg().await.chat_id;
-    let contacts = get_chat_contacts(&bob, bob_chat_id).await?;
-    assert_eq!(contacts.len(), 2);
-
-    // Bob receives partial message.
-    let msg_id = receive_imf_from_inbox(
-        &bob,
-        "first@example.org",
-        b"From: Alice <alice@example.org>\n\
-To: <bob@example.net>, <charlie@example.com>\n\
-Chat-Version: 1.0\n\
-Subject: subject\n\
-Message-ID: <first@example.org>\n\
-Date: Sun, 14 Nov 2021 00:10:00 +0000\
-Content-Type: text/plain
-Chat-Group-Member-Added: charlie@example.com",
-        false,
-        Some(100000),
-    )
-    .await?
-    .context("no received message")?;
-
-    let msg = Message::load_from_db(&bob, msg_id.msg_ids[0]).await?;
-
-    // Partial download does not change the member list.
-    assert_eq!(msg.download_state, DownloadState::Available);
-    assert_eq!(get_chat_contacts(&bob, bob_chat_id).await?, contacts);
-
-    // Alice sends normal message to bob, adding fiona.
-    add_contact_to_chat(
-        &alice,
-        alice_chat_id,
-        alice.add_or_lookup_contact_id(&fiona).await,
-    )
-    .await?;
-
-    bob.recv_msg(&alice.pop_sent_msg().await).await;
-
-    let contacts = get_chat_contacts(&bob, bob_chat_id).await?;
-    assert_eq!(contacts.len(), 3);
-
-    // Bob fully receives the partial message.
-    let msg_id = receive_imf_from_inbox(
-        &bob,
-        "first@example.org",
-        b"From: Alice <alice@example.org>\n\
-To: Bob <bob@example.net>\n\
-Chat-Version: 1.0\n\
-Subject: subject\n\
-Message-ID: <first@example.org>\n\
-Date: Sun, 14 Nov 2021 00:10:00 +0000\
-Content-Type: text/plain
-Chat-Group-Member-Added: charlie@example.com",
-        false,
-        None,
-    )
-    .await?
-    .context("no received message")?;
-
-    let msg = Message::load_from_db(&bob, msg_id.msg_ids[0]).await?;
-
-    // After full download, the old message should not change group state.
-    assert_eq!(msg.download_state, DownloadState::Done);
-    assert_eq!(get_chat_contacts(&bob, bob_chat_id).await?, contacts);
-
-    Ok(())
-}
-
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_protected_group_add_remove_member_missing_key() -> Result<()> {
     let mut tcm = TestContextManager::new();
@@ -4844,48 +4654,6 @@ async fn test_references() -> Result<()> {
     Ok(())
 }
 
-#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn test_prefer_references_to_downloaded_msgs() -> Result<()> {
-    let mut tcm = TestContextManager::new();
-    let alice = &tcm.alice().await;
-    let bob = &tcm.bob().await;
-    bob.set_config(Config::DownloadLimit, Some("1")).await?;
-    let fiona = &tcm.fiona().await;
-    let alice_bob_id = tcm.send_recv(bob, alice, "hi").await.from_id;
-    let alice_fiona_id = tcm.send_recv(fiona, alice, "hi").await.from_id;
-    let alice_chat_id = create_group(alice, "Group").await?;
-    add_contact_to_chat(alice, alice_chat_id, alice_bob_id).await?;
-    // W/o fiona the test doesn't work -- the last message is assigned to the 1:1 chat due to
-    // `is_probably_private_reply()`.
-    add_contact_to_chat(alice, alice_chat_id, alice_fiona_id).await?;
-    let sent = alice.send_text(alice_chat_id, "Hi").await;
-    let received = bob.recv_msg(&sent).await;
-    assert_eq!(received.download_state, DownloadState::Done);
-    let bob_chat_id = received.chat_id;
-
-    let file_bytes = include_bytes!("../../test-data/image/screenshot.gif");
-    let mut msg = Message::new(Viewtype::File);
-    msg.set_file_from_bytes(alice, "file", file_bytes, None)?;
-    let mut sent = alice.send_msg(alice_chat_id, &mut msg).await;
-    sent.payload = sent
-        .payload
-        .replace("References:", "X-Microsoft-Original-References:")
-        .replace("In-Reply-To:", "X-Microsoft-Original-In-Reply-To:");
-    let received = bob.recv_msg(&sent).await;
-    assert_eq!(received.download_state, DownloadState::Available);
-    assert_ne!(received.chat_id, bob_chat_id);
-    assert_eq!(received.chat_id, bob.get_chat(alice).await.id);
-
-    let mut msg = Message::new(Viewtype::File);
-    msg.set_file_from_bytes(alice, "file", file_bytes, None)?;
-    let sent = alice.send_msg(alice_chat_id, &mut msg).await;
-    let received = bob.recv_msg(&sent).await;
-    assert_eq!(received.download_state, DownloadState::Available);
-    assert_eq!(received.chat_id, bob_chat_id);
-
-    Ok(())
-}
-
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_list_from() -> Result<()> {
     let t = &TestContext::new_alice().await;
@@ -5363,41 +5131,6 @@ async fn test_outgoing_plaintext_two_member_group() -> Result<()> {
     Ok(())
 }
 
-/// Tests that large messages are assigned
-/// to non-key-contacts if the type is not `multipart/encrypted`.
-#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn test_partial_download_key_contact_lookup() -> Result<()> {
-    let mut tcm = TestContextManager::new();
-    let alice = &tcm.alice().await;
-    let bob = &tcm.bob().await;
-
-    // Create two chats with Alice, both with key-contact and email address contact.
-    let encrypted_chat = bob.create_chat(alice).await;
-    let unencrypted_chat = bob.create_email_chat(alice).await;
-
-    let seen = false;
-    let is_partial_download = Some(9999);
-    let received = receive_imf_from_inbox(
-        bob,
-        "3333@example.org",
-        b"From: alice@example.org\n\
-        To: bob@example.net\n\
-        Message-ID: <3333@example.org>\n\
-        Date: Sun, 22 Mar 2020 22:37:57 +0000\n\
-        \n\
-        hello\n",
-        seen,
-        is_partial_download,
-    )
-    .await?
-    .unwrap();
-
-    assert_ne!(received.chat_id, encrypted_chat.id);
-    assert_eq!(received.chat_id, unencrypted_chat.id);
-
-    Ok(())
-}
-
 /// Tests that outgoing unencrypted message
 /// is assigned to a chat with email-contact.
 ///

src/scheduler.rs

@@ -14,13 +14,12 @@ pub(crate) use self::connectivity::ConnectivityStore;
 use crate::config::{self, Config};
 use crate::contact::{ContactId, RecentlySeenLoop};
 use crate::context::Context;
-use crate::download::{DownloadState, download_msg};
+use crate::download::{download_known_post_messages_without_pre_message, download_msgs};
 use crate::ephemeral::{self, delete_expired_imap_messages};
 use crate::events::EventType;
 use crate::imap::{FolderMeaning, Imap, session::Session};
 use crate::location;
 use crate::log::{LogExt, warn};
-use crate::message::MsgId;
 use crate::smtp::{Smtp, send_smtp_messages};
 use crate::sql;
 use crate::stats::maybe_send_stats;
@@ -349,38 +348,6 @@ pub(crate) struct Scheduler {
     recently_seen_loop: RecentlySeenLoop,
 }
 
-async fn download_msgs(context: &Context, session: &mut Session) -> Result<()> {
-    let msg_ids = context
-        .sql
-        .query_map_vec("SELECT msg_id FROM download", (), |row| {
-            let msg_id: MsgId = row.get(0)?;
-            Ok(msg_id)
-        })
-        .await?;
-
-    for msg_id in msg_ids {
-        if let Err(err) = download_msg(context, msg_id, session).await {
-            warn!(context, "Failed to download message {msg_id}: {:#}.", err);
-
-            // Update download state to failure
-            // so it can be retried.
-            //
-            // On success update_download_state() is not needed
-            // as receive_imf() already
-            // set the state and emitted the event.
-            msg_id
-                .update_download_state(context, DownloadState::Failure)
-                .await?;
-        }
-        context
-            .sql
-            .execute("DELETE FROM download WHERE msg_id=?", (msg_id,))
-            .await?;
-    }
-
-    Ok(())
-}
-
 async fn inbox_loop(
     ctx: Context,
     started: oneshot::Sender<()>,
@@ -606,7 +573,7 @@ async fn fetch_idle(
     {
         // Fetch the watched folder.
         connection
-            .fetch_move_delete(ctx, &mut session, &watch_folder, folder_meaning)
+            .fetch_move_delete(ctx, &mut session, true, &watch_folder, folder_meaning)
             .await
             .context("fetch_move_delete")?;
 
@@ -617,6 +584,11 @@ async fn fetch_idle(
         delete_expired_imap_messages(ctx)
             .await
             .context("delete_expired_imap_messages")?;
+
+        //-------
+        // TODO: verify that this is the correct position for this call
+        // in order to guard against lost pre-messages:
+        download_known_post_messages_without_pre_message(ctx, &mut session).await?;
     } else if folder_config == Config::ConfiguredInboxFolder {
         session.last_full_folder_scan.lock().await.take();
     }
@@ -645,7 +617,7 @@ async fn fetch_idle(
                 // no new messages. We want to select the watched folder anyway before going IDLE
                 // there, so this does not take additional protocol round-trip.
                 connection
-                    .fetch_move_delete(ctx, &mut session, &watch_folder, folder_meaning)
+                    .fetch_move_delete(ctx, &mut session, true, &watch_folder, folder_meaning)
                     .await
                     .context("fetch_move_delete after scan_folders")?;
             }
@@ -702,6 +674,7 @@ async fn fetch_idle(
     Ok(session)
 }
 
+/// The simplified IMAP IDLE loop to watch non primary folders (non-inbox folders)
 async fn simple_imap_loop(
     ctx: Context,
     started: oneshot::Sender<()>,

src/sql/migrations.rs

@@ -1504,6 +1504,26 @@ ORDER BY last_seen DESC LIMIT 10000
             .await?;
     }
 
+    inc_and_check(&mut migration_version, 144)?;
+    if dbversion < migration_version {
+        sql.execute_migration(
+            "CREATE TABLE download_new (
+                rfc724_mid TEXT NOT NULL
+            );
+            INSERT INTO download_new (rfc724_mid)
+             SELECT m.rfc724_mid FROM download d
+             JOIN msgs m ON d.msg_id = m.id
+             WHERE m.rfc724_mid IS NOT NULL AND m.rfc724_mid != '';
+            DROP TABLE download;
+            ALTER TABLE download_new RENAME TO download;
+            CREATE TABLE available_post_msgs (
+                rfc724_mid TEXT NOT NULL
+            );",
+            migration_version,
+        )
+        .await?;
+    }
+
     let new_version = sql
         .get_raw_config_int(VERSION_CFG)
         .await?

src/stock_str.rs

@@ -4,7 +4,6 @@ use std::collections::HashMap;
 use std::sync::Arc;
 
 use anyhow::{Result, bail};
-use humansize::{BINARY, format_size};
 use strum::EnumProperty as EnumPropertyTrait;
 use strum_macros::EnumProperty;
 use tokio::sync::RwLock;
@@ -17,7 +16,6 @@ use crate::contact::{Contact, ContactId};
 use crate::context::Context;
 use crate::message::{Message, Viewtype};
 use crate::param::Param;
-use crate::tools::timestamp_to_str;
 
 /// Storage for string translations.
 #[derive(Debug, Clone)]
@@ -170,9 +168,6 @@ pub enum StockMessage {
     #[strum(props(fallback = "%1$s message"))]
     PartialDownloadMsgBody = 99,
 
-    #[strum(props(fallback = "Download maximum available until %1$s"))]
-    DownloadAvailability = 100,
-
     #[strum(props(fallback = "Multi Device Synchronization"))]
     SyncMsgSubject = 101,
 
@@ -1119,21 +1114,6 @@ pub(crate) async fn quota_exceeding(context: &Context, highest_usage: u64) -> St
         .replace("%%", "%")
 }
 
-/// Stock string: `%1$s message` with placeholder replaced by human-readable size.
-pub(crate) async fn partial_download_msg_body(context: &Context, org_bytes: u32) -> String {
-    let size = &format_size(org_bytes, BINARY);
-    translated(context, StockMessage::PartialDownloadMsgBody)
-        .await
-        .replace1(size)
-}
-
-/// Stock string: `Download maximum available until %1$s`.
-pub(crate) async fn download_availability(context: &Context, timestamp: i64) -> String {
-    translated(context, StockMessage::DownloadAvailability)
-        .await
-        .replace1(&timestamp_to_str(timestamp))
-}
-
 /// Stock string: `Incoming Messages`.
 pub(crate) async fn incoming_messages(context: &Context) -> String {
     translated(context, StockMessage::IncomingMessages).await
@@ -1262,6 +1242,26 @@ pub(crate) async fn chat_unencrypted_explanation(context: &Context) -> String {
     translated(context, StockMessage::ChatUnencryptedExplanation).await
 }
 
+impl Viewtype {
+    /// returns Localized name for message viewtype
+    pub async fn to_locale_string(&self, context: &Context) -> String {
+        match self {
+            Viewtype::Image => image(context).await,
+            Viewtype::Gif => gif(context).await,
+            Viewtype::Sticker => sticker(context).await,
+            Viewtype::Audio => audio(context).await,
+            Viewtype::Voice => voice_message(context).await,
+            Viewtype::Video => video(context).await,
+            Viewtype::File => file(context).await,
+            Viewtype::Webxdc => "Mini App".to_owned(), // TODO stock-string
+            Viewtype::Vcard => "Contact".to_owned(),   // TODO stock-string
+            // OPTIONAL TODO - would not be used right now,
+            // because this method is only used for metadata on large attachments
+            Viewtype::Unknown | Viewtype::Text | Viewtype::Call => self.to_string(),
+        }
+    }
+}
+
 impl Context {
     /// Set the stock string for the [StockMessage].
     ///

src/stock_str/stock_str_tests.rs

@@ -118,14 +118,6 @@ async fn test_quota_exceeding_stock_str() -> Result<()> {
     Ok(())
 }
 
-#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn test_partial_download_msg_body() -> Result<()> {
-    let t = TestContext::new().await;
-    let str = partial_download_msg_body(&t, 1024 * 1024).await;
-    assert_eq!(str, "1 MiB message");
-    Ok(())
-}
-
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_update_device_chats() {
     let t = TestContext::new_alice().await;

src/test_utils.rs

@@ -711,6 +711,32 @@ impl TestContext {
         })
     }
 
+    pub async fn get_smtp_rows_for_msg<'a>(&'a self, msg_id: MsgId) -> Vec<SentMessage<'a>> {
+        self.ctx
+            .sql
+            .query_map_vec(
+                "SELECT id, msg_id, mime, recipients FROM smtp WHERE msg_id=?",
+                (msg_id,),
+                |row| {
+                    let _id: MsgId = row.get(0)?;
+                    let msg_id: MsgId = row.get(1)?;
+                    let mime: String = row.get(2)?;
+                    let recipients: String = row.get(3)?;
+                    Ok((msg_id, mime, recipients))
+                },
+            )
+            .await
+            .unwrap()
+            .into_iter()
+            .map(|(msg_id, mime, recipients)| SentMessage {
+                payload: mime,
+                sender_msg_id: msg_id,
+                sender_context: &self.ctx,
+                recipients,
+            })
+            .collect()
+    }
+
     /// Retrieves a sent sync message from the db.
     ///
     /// This retrieves and removes a sync message which has been scheduled to send from the jobs
@@ -759,7 +785,7 @@ impl TestContext {
     /// unlikely to be affected as the message would be processed again in exactly the
     /// same way.
     pub(crate) async fn parse_msg(&self, msg: &SentMessage<'_>) -> MimeMessage {
-        MimeMessage::from_bytes(&self.ctx, msg.payload().as_bytes(), None)
+        MimeMessage::from_bytes(&self.ctx, msg.payload().as_bytes())
             .await
             .unwrap()
     }
@@ -1693,6 +1719,21 @@ Until the false-positive is fixed:
     }
 }
 
+/// Method to create a test image file
+pub(crate) fn create_test_image(width: u32, height: u32) -> anyhow::Result<Vec<u8>> {
+    use image::{ImageBuffer, Rgb, RgbImage};
+    use std::io::Cursor;
+
+    let mut img: RgbImage = ImageBuffer::new(width, height);
+    // fill with some pattern so it stays large after compression
+    for (x, y, pixel) in img.enumerate_pixels_mut() {
+        *pixel = Rgb([(x % 255) as u8, (x + y % 255) as u8, (y % 255) as u8]);
+    }
+    let mut bytes: Vec<u8> = Vec::new();
+    img.write_to(&mut Cursor::new(&mut bytes), image::ImageFormat::Png)?;
+    Ok(bytes)
+}
+
 mod tests {
     use super::*;
 

src/tests.rs

@@ -1,3 +1,4 @@
 mod account_events;
 mod aeap;
+mod pre_messages;
 mod verified_chats;

src/tests/pre_messages/additional_text.rs

@@ -0,0 +1,115 @@
+use anyhow::Result;
+use pretty_assertions::assert_eq;
+
+use crate::EventType;
+use crate::config::Config;
+use crate::imex::{ImexMode, has_backup, imex};
+use crate::message::{Message, Viewtype};
+use crate::test_utils::TestContextManager;
+use crate::tests::pre_messages::util::{
+    send_large_file_message, send_large_image_message, send_large_webxdc_message,
+};
+
+/// Test the addition of the download info to message text
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_additional_text_on_different_viewtypes() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let a_group_id = alice.create_group_with_members("test group", &[bob]).await;
+
+    tcm.section("Test metadata preview text for File");
+    let (pre_message, _, _) =
+        send_large_file_message(alice, a_group_id, Viewtype::File, &vec![0u8; 1_000_000]).await?;
+    let msg = bob.recv_msg(&pre_message).await;
+    assert_eq!(msg.text, "test".to_owned());
+    assert_eq!(msg.get_text(), "test [test.bin - 976.56 KiB]".to_owned());
+
+    tcm.section("Test metadata preview text for webxdc app");
+    let (pre_message, _, _) = send_large_webxdc_message(alice, a_group_id).await?;
+    let msg = bob.recv_msg(&pre_message).await;
+    assert_eq!(msg.text, "test".to_owned());
+    assert_eq!(msg.get_post_message_viewtype(), Some(Viewtype::Webxdc));
+    assert_eq!(msg.get_text(), "test [Mini App - 976.68 KiB]".to_owned());
+
+    tcm.section("Test metadata preview text for Image");
+
+    let (pre_message, _, _) = send_large_image_message(alice, a_group_id).await?;
+    let msg = bob.recv_msg(&pre_message).await;
+    assert_eq!(msg.text, "test".to_owned());
+    assert_eq!(msg.get_text(), "test [Image - 146.12 KiB]".to_owned());
+
+    Ok(())
+}
+
+/// Test that disabling the addition of the download info works
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_disable_additional_text() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let alice_group_id = alice.create_group_with_members("test group", &[bob]).await;
+
+    let (pre_message, _post_message, _alice_msg_id) =
+        send_large_file_message(alice, alice_group_id, Viewtype::File, &vec![0u8; 1_000_000])
+            .await?;
+    let msg = bob.recv_msg(&pre_message).await;
+    assert_eq!(msg.get_text(), "test [test.bin - 976.56 KiB]".to_owned());
+
+    bob.set_config_bool(Config::HidePreMessageMetadataText, true)
+        .await?;
+
+    let msg = Message::load_from_db(bob, msg.id).await?;
+    assert_eq!(msg.get_text(), "test".to_owned());
+    Ok(())
+}
+
+/// Test that disabling the addition of the download info works
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_disable_option_is_exluded_from_backup() -> Result<()> {
+    let backup_dir = tempfile::tempdir()?;
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+
+    tcm.section("set config option");
+    alice
+        .set_config_bool(Config::HidePreMessageMetadataText, true)
+        .await?;
+    assert_eq!(
+        alice
+            .get_config_bool(Config::HidePreMessageMetadataText)
+            .await?,
+        true
+    );
+
+    tcm.section("export backup");
+    imex(alice, ImexMode::ExportBackup, backup_dir.path(), None).await?;
+    let _event = alice
+        .evtracker
+        .get_matching(|evt| matches!(evt, EventType::ImexProgress(1000)))
+        .await;
+
+    tcm.section("import backup");
+    let alice2 = &tcm.unconfigured().await;
+    let backup = has_backup(alice2, backup_dir.path()).await?;
+    imex(alice2, ImexMode::ImportBackup, backup.as_ref(), None).await?;
+    let _event = alice2
+        .evtracker
+        .get_matching(|evt| matches!(evt, EventType::ImexProgress(1000)))
+        .await;
+    assert_eq!(
+        alice.get_primary_self_addr().await?,
+        alice2.get_primary_self_addr().await?,
+        "address should be the same"
+    );
+
+    tcm.section("test if config is reset as expected");
+    assert_eq!(
+        alice2
+            .get_config_bool(Config::HidePreMessageMetadataText)
+            .await?,
+        false
+    );
+
+    Ok(())
+}

src/tests/pre_messages/forward_and_save.rs

@@ -0,0 +1,122 @@
+//! Tests about forwarding and saving Pre-Messages
+use anyhow::Result;
+use pretty_assertions::assert_eq;
+
+use crate::chat::{self};
+use crate::chat::{forward_msgs, save_msgs};
+use crate::chatlist::get_last_message_for_chat;
+use crate::download::{DownloadState, PRE_MSG_ATTACHMENT_SIZE_THRESHOLD};
+use crate::message::{Message, Viewtype};
+use crate::test_utils::TestContextManager;
+
+/// Test that forwarding Pre-Message should forward additional text to not be empty
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_forwarding_pre_message_empty_text() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let alice_group_id = alice.create_group_with_members("test group", &[bob]).await;
+
+    let pre_message = {
+        let mut msg = Message::new(Viewtype::File);
+        msg.set_file_from_bytes(alice, "test.bin", &vec![0u8; 1_000_000], None)?;
+        assert!(msg.get_filebytes(alice).await?.unwrap() > PRE_MSG_ATTACHMENT_SIZE_THRESHOLD);
+        let msg_id = chat::send_msg(alice, alice_group_id, &mut msg).await?;
+        let smtp_rows = alice.get_smtp_rows_for_msg(msg_id).await;
+        assert_eq!(smtp_rows.len(), 2);
+        smtp_rows.first().expect("Pre-Message exists").to_owned()
+    };
+
+    let bob_msg = bob.recv_msg(&pre_message).await;
+    assert_eq!(bob_msg.download_state, DownloadState::Available);
+    bob_msg.chat_id.accept(bob).await?;
+    tcm.section("forward pre message and check it on bobs side");
+    forward_msgs(bob, &[bob_msg.id], bob_msg.chat_id).await?;
+    let forwarded_msg_id = get_last_message_for_chat(bob, bob_msg.chat_id)
+        .await?
+        .unwrap();
+    let forwarded_msg = Message::load_from_db(bob, forwarded_msg_id).await?;
+    assert_eq!(forwarded_msg.is_forwarded(), true);
+    assert_eq!(forwarded_msg.download_state(), DownloadState::Done);
+    assert_eq!(
+        forwarded_msg
+            .param
+            .exists(crate::param::Param::PostMessageFileBytes),
+        false,
+        "PostMessageFileBytes not set"
+    );
+    assert_eq!(
+        forwarded_msg
+            .param
+            .exists(crate::param::Param::PostMessageViewtype),
+        false,
+        "PostMessageViewtype not set"
+    );
+    assert_eq!(
+        forwarded_msg.get_text(),
+        " [test.bin - 976.56 KiB]".to_owned()
+    );
+    assert_eq!(forwarded_msg.get_viewtype(), Viewtype::Text);
+    assert!(forwarded_msg.additional_text.is_empty());
+    tcm.section("check it on alices side");
+    let sent_forward_msg = bob.pop_sent_msg().await;
+    let alice_forwarded_msg = alice.recv_msg(&sent_forward_msg).await;
+    assert!(alice_forwarded_msg.additional_text.is_empty());
+    assert_eq!(alice_forwarded_msg.is_forwarded(), true);
+    assert_eq!(alice_forwarded_msg.download_state(), DownloadState::Done);
+    assert_eq!(
+        alice_forwarded_msg
+            .param
+            .exists(crate::param::Param::PostMessageFileBytes),
+        false,
+        "PostMessageFileBytes not set"
+    );
+    assert_eq!(
+        alice_forwarded_msg
+            .param
+            .exists(crate::param::Param::PostMessageViewtype),
+        false,
+        "PostMessageViewtype not set"
+    );
+    assert_eq!(
+        alice_forwarded_msg.get_text(),
+        " [test.bin - 976.56 KiB]".to_owned()
+    );
+
+    Ok(())
+}
+
+/// Test that forwarding Pre-Message should forward additional text to not be empty
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_saving_pre_message_empty_text() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let alice_group_id = alice.create_group_with_members("test group", &[bob]).await;
+
+    let pre_message = {
+        let mut msg = Message::new(Viewtype::File);
+        msg.set_file_from_bytes(alice, "test.bin", &vec![0u8; 1_000_000], None)?;
+        assert!(msg.get_filebytes(alice).await?.unwrap() > PRE_MSG_ATTACHMENT_SIZE_THRESHOLD);
+        let msg_id = chat::send_msg(alice, alice_group_id, &mut msg).await?;
+        let smtp_rows = alice.get_smtp_rows_for_msg(msg_id).await;
+        assert_eq!(smtp_rows.len(), 2);
+        smtp_rows.first().expect("Pre-Message exists").to_owned()
+    };
+
+    let bob_msg = bob.recv_msg(&pre_message).await;
+    assert_eq!(bob_msg.download_state, DownloadState::Available);
+    bob_msg.chat_id.accept(bob).await?;
+    tcm.section("save pre message and check it");
+    save_msgs(bob, &[bob_msg.id]).await?;
+    let saved_msg_id = get_last_message_for_chat(bob, bob.get_self_chat().await.id)
+        .await?
+        .unwrap();
+    let saved_msg = Message::load_from_db(bob, saved_msg_id).await?;
+    assert!(saved_msg.additional_text.is_empty());
+    assert!(saved_msg.get_original_msg_id(bob).await?.is_some());
+    assert_eq!(saved_msg.download_state(), DownloadState::Done);
+    assert_eq!(saved_msg.get_text(), " [test.bin - 976.56 KiB]".to_owned());
+
+    Ok(())
+}

src/tests/pre_messages/legacy.rs

@@ -0,0 +1,61 @@
+//! Test that downloading old stub messages still works
+use anyhow::Result;
+
+use crate::download::DownloadState;
+use crate::receive_imf::receive_imf_from_inbox;
+use crate::test_utils::TestContext;
+
+// The code for downloading stub messages stays
+// during the transition perios to pre-messages
+// so people can still download their files shortly after they updated.
+// After there are a few release with pre-message rolled out,
+// we will remove the ability to download stub messages and replace the following test
+// so it checks that it doesn't crash or that the messages are replaced by sth.
+// like "download failed/expired, please ask sender to send it again"
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_download_stub_message() -> Result<()> {
+    let t = TestContext::new_alice().await;
+
+    let header = "Received: (Postfix, from userid 1000); Mon, 4 Dec 2006 14:51:39 +0100 (CET)\n\
+             From: bob@example.com\n\
+             To: alice@example.org\n\
+             Subject: foo\n\
+             Message-ID: <Mr.12345678901@example.com>\n\
+             Chat-Version: 1.0\n\
+             Date: Sun, 22 Mar 2020 22:37:57 +0000\
+             Content-Type: text/plain";
+
+    t.sql
+        .execute(
+            r#"INSERT INTO chats VALUES(
+                    11001,100,'bob@example.com',0,'',2,'',
+                    replace('C=1763151754\nt=foo','\n',char(10)),0,0,0,0,0,1763151754,0,NULL,0,'');
+                "#,
+            (),
+        )
+        .await?;
+    t.sql.execute(r#"INSERT INTO msgs VALUES(
+                11001,'Mr.12345678901@example.com','',0,
+                11001,11001,1,1763151754,10,10,1,0,
+                '[97.66 KiB message]','','',0,1763151754,1763151754,0,X'',
+                '','',1,0,'',0,0,0,'foo',10,replace('Hop: From: userid; Date: Mon, 4 Dec 2006 13:51:39 +0000\n\nDKIM Results: Passed=true','\n',char(10)),1,NULL,0);
+        "#, ()).await?;
+    let msg = t.get_last_msg().await;
+    assert_eq!(msg.download_state(), DownloadState::Available);
+    assert_eq!(msg.get_subject(), "foo");
+    assert!(msg.get_text().contains("[97.66 KiB message]"));
+
+    receive_imf_from_inbox(
+        &t,
+        "Mr.12345678901@example.com",
+        format!("{header}\n\n100k text...").as_bytes(),
+        false,
+    )
+    .await?;
+    let msg = t.get_last_msg().await;
+    assert_eq!(msg.download_state(), DownloadState::Done);
+    assert_eq!(msg.get_subject(), "foo");
+    assert_eq!(msg.get_text(), "100k text...");
+
+    Ok(())
+}

src/tests/pre_messages/mod.rs

@@ -0,0 +1,6 @@
+mod additional_text;
+mod forward_and_save;
+mod legacy;
+mod receiving;
+mod sending;
+mod util;

src/tests/pre_messages/receiving.rs

@@ -0,0 +1,522 @@
+//! Tests about receiving Pre-Messages and Post-Message
+use anyhow::Result;
+use pretty_assertions::assert_eq;
+
+use crate::EventType;
+use crate::chat;
+use crate::contact;
+use crate::download::{
+    DownloadState, PRE_MSG_ATTACHMENT_SIZE_THRESHOLD, pre_msg_metadata::PreMsgMetadata,
+};
+use crate::message::{Message, MessageState, Viewtype, delete_msgs, markseen_msgs};
+use crate::mimeparser::MimeMessage;
+use crate::param::Param;
+use crate::reaction::{get_msg_reactions, send_reaction};
+use crate::test_utils::TestContextManager;
+use crate::tests::pre_messages::util::{
+    send_large_file_message, send_large_image_message, send_large_webxdc_message,
+};
+use crate::webxdc::StatusUpdateSerial;
+
+/// Test that mimeparser can correctly detect and parse pre-messages and Post-Messages
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_mimeparser_pre_message_and_post_message() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let alice_group_id = alice.create_group_with_members("test group", &[bob]).await;
+
+    let (pre_message, post_message, _alice_msg_id) =
+        send_large_file_message(alice, alice_group_id, Viewtype::File, &vec![0u8; 1_000_000])
+            .await?;
+
+    let parsed_pre_message = MimeMessage::from_bytes(bob, pre_message.payload.as_bytes()).await?;
+    let parsed_post_message = MimeMessage::from_bytes(bob, post_message.payload.as_bytes()).await?;
+
+    assert_eq!(
+        parsed_post_message.pre_message,
+        Some(crate::mimeparser::PreMessageMode::PostMessage)
+    );
+
+    assert_eq!(
+        parsed_pre_message.pre_message,
+        Some(crate::mimeparser::PreMessageMode::PreMessage {
+            post_msg_rfc724_mid: parsed_post_message.get_rfc724_mid().unwrap(),
+            metadata: Some(PreMsgMetadata {
+                size: 1_000_000,
+                viewtype: Viewtype::File,
+                filename: "test.bin".to_string(),
+                dimensions: None,
+                duration: None
+            })
+        })
+    );
+
+    Ok(())
+}
+
+/// Test receiving pre-messages and creation of the placeholder message with the metadata
+/// for file attachment
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_receive_pre_message() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let alice_group_id = alice.create_group_with_members("test group", &[bob]).await;
+
+    let (pre_message, _post_message, _alice_msg_id) =
+        send_large_file_message(alice, alice_group_id, Viewtype::File, &vec![0u8; 1_000_000])
+            .await?;
+
+    let msg = bob.recv_msg(&pre_message).await;
+
+    assert_eq!(msg.download_state(), DownloadState::Available);
+    assert_eq!(msg.viewtype, Viewtype::Text);
+    assert_eq!(msg.text, "test".to_owned());
+
+    // test that metadata is correctly returned by methods
+    assert_eq!(msg.get_filebytes(bob).await?, Some(1_000_000));
+    assert_eq!(msg.get_post_message_viewtype(), Some(Viewtype::File));
+    assert_eq!(msg.get_filename(), Some("test.bin".to_owned()));
+
+    Ok(())
+}
+
+/// Test receiving the Post-Message after receiving the pre-message
+/// for file attachment
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_receive_pre_message_and_dl_post_message() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let alice_group_id = alice.create_group_with_members("test group", &[bob]).await;
+
+    let (pre_message, post_message, _alice_msg_id) =
+        send_large_file_message(alice, alice_group_id, Viewtype::File, &vec![0u8; 1_000_000])
+            .await?;
+
+    let msg = bob.recv_msg(&pre_message).await;
+    assert_eq!(msg.download_state(), DownloadState::Available);
+    assert_eq!(msg.viewtype, Viewtype::Text);
+    assert!(msg.param.exists(Param::PostMessageViewtype));
+    assert!(msg.param.exists(Param::PostMessageFileBytes));
+    assert_eq!(msg.text, "test".to_owned());
+    let _ = bob.recv_msg_trash(&post_message).await;
+    let msg = Message::load_from_db(bob, msg.id).await?;
+    assert_eq!(msg.download_state(), DownloadState::Done);
+    assert_eq!(msg.viewtype, Viewtype::File);
+    assert_eq!(msg.param.exists(Param::PostMessageViewtype), false);
+    assert_eq!(msg.param.exists(Param::PostMessageFileBytes), false);
+    assert_eq!(msg.text, "test".to_owned());
+    Ok(())
+}
+
+/// Test out of order receiving. Post-Message is received & downloaded before pre-message.
+/// In that case pre-message shall be trashed.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_out_of_order_receiving() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let alice_group_id = alice.create_group_with_members("test group", &[bob]).await;
+
+    let (pre_message, post_message, _alice_msg_id) =
+        send_large_file_message(alice, alice_group_id, Viewtype::File, &vec![0u8; 1_000_000])
+            .await?;
+
+    let msg = bob.recv_msg(&post_message).await;
+    assert_eq!(msg.download_state(), DownloadState::Done);
+    assert_eq!(msg.viewtype, Viewtype::File);
+    let _ = bob.recv_msg_trash(&pre_message).await;
+    Ok(())
+}
+
+/// Test receiving the Post-Message after receiving an edit after receiving the pre-message
+/// for file attachment
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_receive_pre_message_then_edit_and_then_dl_post_message() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let alice_group_id = alice.create_group_with_members("test group", &[bob]).await;
+
+    let (pre_message, post_message, alice_msg_id) =
+        send_large_file_message(alice, alice_group_id, Viewtype::File, &vec![0u8; 1_000_000])
+            .await?;
+
+    chat::send_edit_request(alice, alice_msg_id, "new_text".to_owned()).await?;
+    let edit_request = alice.pop_sent_msg().await;
+
+    let msg = bob.recv_msg(&pre_message).await;
+    assert_eq!(msg.download_state(), DownloadState::Available);
+    assert_eq!(msg.text, "test".to_owned());
+    let _ = bob.recv_msg_trash(&edit_request).await;
+    let msg = Message::load_from_db(bob, msg.id).await?;
+    assert_eq!(msg.download_state(), DownloadState::Available);
+    assert_eq!(msg.text, "new_text".to_owned());
+    let _ = bob.recv_msg_trash(&post_message).await;
+    let msg = Message::load_from_db(bob, msg.id).await?;
+    assert_eq!(msg.download_state(), DownloadState::Done);
+    assert_eq!(msg.viewtype, Viewtype::File);
+    assert_eq!(msg.text, "new_text".to_owned());
+    Ok(())
+}
+
+/// Process normal message with file attachment (neither post nor pre message)
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_receive_normal_message() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let alice_group_id = alice.create_group_with_members("test group", &[bob]).await;
+
+    let mut msg = Message::new(Viewtype::File);
+    msg.set_file_from_bytes(
+        alice,
+        "test.bin",
+        &vec![0u8; (PRE_MSG_ATTACHMENT_SIZE_THRESHOLD - 10_000) as usize],
+        None,
+    )?;
+    msg.set_text("test".to_owned());
+    let msg_id = chat::send_msg(alice, alice_group_id, &mut msg).await?;
+
+    let smtp_rows = alice.get_smtp_rows_for_msg(msg_id).await;
+    assert_eq!(smtp_rows.len(), 1);
+    let message = smtp_rows.first().expect("message exists");
+
+    let msg = bob.recv_msg(message).await;
+    assert_eq!(msg.download_state(), DownloadState::Done);
+    assert_eq!(msg.viewtype, Viewtype::File);
+    assert_eq!(msg.text, "test".to_owned());
+    Ok(())
+}
+
+/// Test receiving pre-messages and creation of the placeholder message with the metadata
+/// for image attachment
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_receive_pre_message_image() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let alice_group_id = alice.create_group_with_members("test group", &[bob]).await;
+
+    let (pre_message, _post_message, _alice_msg_id) =
+        send_large_image_message(alice, alice_group_id).await?;
+
+    let msg = bob.recv_msg(&pre_message).await;
+
+    assert_eq!(msg.download_state(), DownloadState::Available);
+    assert_eq!(msg.viewtype, Viewtype::Text);
+    assert_eq!(msg.text, "test".to_owned());
+
+    // test that metadata is correctly returned by methods
+    assert_eq!(msg.get_post_message_viewtype(), Some(Viewtype::Image));
+    // recoded image dimensions
+    assert_eq!(msg.get_filebytes(bob).await?, Some(149632));
+    assert_eq!(msg.get_height(), 1280);
+    assert_eq!(msg.get_width(), 720);
+
+    Ok(())
+}
+
+/// Test receiving reaction on pre-message
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_reaction_on_pre_message() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let alice_group_id = alice.create_group_with_members("test group", &[bob]).await;
+
+    let (pre_message, post_message, alice_msg_id) =
+        send_large_file_message(alice, alice_group_id, Viewtype::File, &vec![0u8; 1_000_000])
+            .await?;
+
+    // Bob receives pre-message
+    let bob_msg = bob.recv_msg(&pre_message).await;
+    assert_eq!(bob_msg.download_state(), DownloadState::Available);
+
+    // Alice sends reaction to her own message
+    send_reaction(alice, alice_msg_id, "👍").await?;
+
+    // Bob receives the reaction
+    bob.recv_msg_hidden(&alice.pop_sent_msg().await).await;
+
+    // Test if Bob sees reaction
+    let reactions = get_msg_reactions(bob, bob_msg.id).await?;
+    assert_eq!(reactions.to_string(), "👍1");
+
+    // Bob downloads Post-Message
+    bob.recv_msg_trash(&post_message).await;
+    let msg = Message::load_from_db(bob, bob_msg.id).await?;
+    assert_eq!(msg.download_state(), DownloadState::Done);
+
+    // Test if Bob still sees reaction
+    let reactions = get_msg_reactions(bob, bob_msg.id).await?;
+    assert_eq!(reactions.to_string(), "👍1");
+
+    Ok(())
+}
+
+/// Tests that fully downloading the message
+/// works but does not reappear when it was already deleted
+/// (as in the Message-ID already exists in the database
+/// and is assigned to the trash chat).
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_full_download_after_trashed() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let bob_group_id = bob.create_group_with_members("test group", &[alice]).await;
+
+    let (pre_message, post_message, _bob_msg_id) =
+        send_large_file_message(bob, bob_group_id, Viewtype::File, &vec![0u8; 1_000_000]).await?;
+
+    // Download message from Bob partially.
+    let alice_msg = alice.recv_msg(&pre_message).await;
+
+    // Delete the received message.
+    // Note that it remains in the database in the trash chat.
+    delete_msgs(alice, &[alice_msg.id]).await?;
+
+    // Fully download message after deletion.
+    alice.recv_msg_trash(&post_message).await;
+
+    // The message does not reappear.
+    let msg = Message::load_from_db_optional(bob, alice_msg.id).await?;
+    assert!(msg.is_none());
+
+    Ok(())
+}
+
+/// Test that webxdc updates are received for pre-messages
+/// and available when the Post-Message is downloaded
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_webxdc_update_for_not_downloaded_instance() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let alice_group_id = alice.create_group_with_members("test group", &[bob]).await;
+
+    // Alice sends a larger instance and an update
+    let (pre_message, post_message, alice_sent_instance_msg_id) =
+        send_large_webxdc_message(alice, alice_group_id).await?;
+    alice
+        .send_webxdc_status_update(
+            alice_sent_instance_msg_id,
+            r#"{"payload": 7, "summary":"sum", "document":"doc"}"#,
+        )
+        .await?;
+    alice.flush_status_updates().await?;
+    let webxdc_update = alice.pop_sent_msg().await;
+
+    // Bob does not download instance but already receives update
+    let bob_instance = bob.recv_msg(&pre_message).await;
+    assert_eq!(bob_instance.download_state, DownloadState::Available);
+    bob.recv_msg_trash(&webxdc_update).await;
+
+    // Bob downloads instance, updates should be assigned correctly
+    bob.recv_msg_trash(&post_message).await;
+
+    let bob_instance = bob.get_last_msg().await;
+    assert_eq!(bob_instance.viewtype, Viewtype::Webxdc);
+    assert_eq!(bob_instance.download_state, DownloadState::Done);
+    assert_eq!(
+        bob.get_webxdc_status_updates(bob_instance.id, StatusUpdateSerial::new(0))
+            .await?,
+        r#"[{"payload":7,"document":"doc","summary":"sum","serial":1,"max_serial":1}]"#
+    );
+    let info = bob_instance.get_webxdc_info(bob).await?;
+    assert_eq!(info.document, "doc");
+    assert_eq!(info.summary, "sum");
+
+    Ok(())
+}
+
+/// Test mark seen pre-message
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_markseen_pre_msg() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let bob_chat_id = bob.create_chat(alice).await.id;
+    alice.create_chat(bob).await; // Make sure the chat is accepted.
+
+    tcm.section("Bob sends a large message to Alice");
+    let (pre_message, post_message, _bob_msg_id) =
+        send_large_file_message(bob, bob_chat_id, Viewtype::File, &vec![0u8; 1_000_000]).await?;
+
+    tcm.section("Alice receives a pre-message message from Bob");
+    let msg = alice.recv_msg(&pre_message).await;
+    assert_eq!(msg.download_state, DownloadState::Available);
+    assert!(msg.param.get_bool(Param::WantsMdn).unwrap_or_default());
+    assert_eq!(msg.state, MessageState::InFresh);
+
+    tcm.section("Alice marks the pre-message as read and sends a MDN");
+    markseen_msgs(alice, vec![msg.id]).await?;
+    assert_eq!(msg.id.get_state(alice).await?, MessageState::InSeen);
+    assert_eq!(
+        alice
+            .sql
+            .count("SELECT COUNT(*) FROM smtp_mdns", ())
+            .await?,
+        1
+    );
+
+    tcm.section("Alice downloads message");
+    alice.recv_msg_trash(&post_message).await;
+    let msg = Message::load_from_db(alice, msg.id).await?;
+    assert_eq!(msg.download_state, DownloadState::Done);
+    assert!(msg.param.get_bool(Param::WantsMdn).unwrap_or_default());
+    assert_eq!(
+        msg.state,
+        MessageState::InSeen,
+        "The message state mustn't be downgraded to `InFresh`"
+    );
+
+    Ok(())
+}
+
+/// Test that pre-message can start a chat
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_pre_msg_can_start_chat() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+
+    tcm.section("establishing a DM chat between alice and bob");
+    let bob_alice_dm_chat_id = bob.create_chat(alice).await.id;
+    alice.create_chat(bob).await; // Make sure the chat is accepted.
+
+    tcm.section("Alice prepares chat");
+    let chat_id = chat::create_group(alice, "my group").await?;
+    let contacts = contact::Contact::get_all(alice, 0, None).await?;
+    let alice_bob_id = contacts.first().expect("contact exists");
+    chat::add_contact_to_chat(alice, chat_id, *alice_bob_id).await?;
+
+    tcm.section("Alice sends large message to promote/start chat");
+    let (pre_message, _post_message, _alice_msg_id) =
+        send_large_file_message(alice, chat_id, Viewtype::File, &vec![0u8; 1_000_000]).await?;
+
+    tcm.section("Bob receives the pre-message message from Alice");
+    let msg = bob.recv_msg(&pre_message).await;
+    assert_eq!(msg.download_state, DownloadState::Available);
+    assert_ne!(msg.chat_id, bob_alice_dm_chat_id);
+    let chat = chat::Chat::load_from_db(bob, msg.chat_id).await?;
+    assert_eq!(chat.name, "my group");
+
+    Ok(())
+}
+
+/// Test that Post-Message can start a chat
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_post_msg_can_start_chat() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+
+    tcm.section("establishing a DM chat between alice and bob");
+    let bob_alice_dm_chat_id = bob.create_chat(alice).await.id;
+    alice.create_chat(bob).await; // Make sure the chat is accepted.
+
+    tcm.section("Alice prepares chat");
+    let chat_id = chat::create_group(alice, "my group").await?;
+    let contacts = contact::Contact::get_all(alice, 0, None).await?;
+    let alice_bob_id = contacts.first().expect("contact exists");
+    chat::add_contact_to_chat(alice, chat_id, *alice_bob_id).await?;
+
+    tcm.section("Alice sends large message to promote/start chat");
+    let (_pre_message, post_message, _bob_msg_id) =
+        send_large_file_message(alice, chat_id, Viewtype::File, &vec![0u8; 1_000_000]).await?;
+
+    tcm.section("Bob receives the pre-message message from Alice");
+    let msg = bob.recv_msg(&post_message).await;
+    assert_eq!(msg.download_state, DownloadState::Done);
+    assert_ne!(msg.chat_id, bob_alice_dm_chat_id);
+    let chat = chat::Chat::load_from_db(bob, msg.chat_id).await?;
+    assert_eq!(chat.name, "my group");
+
+    Ok(())
+}
+
+/// Test that message ordering is still correct after downloading
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_download_later_keeps_message_order() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+
+    tcm.section(
+        "establishing a DM chat between alice and bob and bob sends large message to alice",
+    );
+    let bob_alice_dm_chat = bob.create_chat(alice).await.id;
+    alice.create_chat(bob).await; // Make sure the chat is accepted.
+    let (pre_message, post_message, _bob_msg_id) = send_large_file_message(
+        bob,
+        bob_alice_dm_chat,
+        Viewtype::File,
+        &vec![0u8; 1_000_000],
+    )
+    .await?;
+
+    tcm.section("Alice downloads pre-message");
+    let msg = alice.recv_msg(&pre_message).await;
+    assert_eq!(msg.download_state, DownloadState::Available);
+    assert_eq!(msg.state, MessageState::InFresh);
+    assert_eq!(alice.get_last_msg_in(msg.chat_id).await.id, msg.id);
+
+    tcm.section("Bob sends hi to Alice");
+    let hi_msg = tcm.send_recv(bob, alice, "hi").await;
+    assert_eq!(alice.get_last_msg_in(msg.chat_id).await.id, hi_msg.id);
+
+    tcm.section("Alice downloads Post-Message");
+    alice.recv_msg_trash(&post_message).await;
+    let msg = Message::load_from_db(alice, msg.id).await?;
+    assert_eq!(msg.download_state, DownloadState::Done);
+    assert_eq!(alice.get_last_msg_in(msg.chat_id).await.id, hi_msg.id);
+    assert!(msg.timestamp_sort <= hi_msg.timestamp_sort);
+
+    Ok(())
+}
+
+/// Test that ChatlistItemChanged event is emitted when downloading Post-Message
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_chatlist_event_on_post_msg_download() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+
+    tcm.section(
+        "establishing a DM chat between alice and bob and bob sends large message to alice",
+    );
+    let bob_alice_dm_chat = bob.create_chat(alice).await.id;
+    alice.create_chat(bob).await; // Make sure the chat is accepted.
+    let (pre_message, post_message, _bob_msg_id) = send_large_file_message(
+        bob,
+        bob_alice_dm_chat,
+        Viewtype::File,
+        &vec![0u8; 1_000_000],
+    )
+    .await?;
+
+    tcm.section("Alice downloads pre-message");
+    let msg = alice.recv_msg(&pre_message).await;
+    assert_eq!(msg.download_state, DownloadState::Available);
+    assert_eq!(msg.state, MessageState::InFresh);
+    assert_eq!(alice.get_last_msg_in(msg.chat_id).await.id, msg.id);
+
+    tcm.section("Alice downloads Post-Message and waits for ChatlistItemChanged event ");
+    alice.evtracker.clear_events();
+    alice.recv_msg_trash(&post_message).await;
+    let msg = Message::load_from_db(alice, msg.id).await?;
+    assert_eq!(msg.download_state, DownloadState::Done);
+    alice
+        .evtracker
+        .get_matching(|e| {
+            e == &EventType::ChatlistItemChanged {
+                chat_id: Some(msg.chat_id),
+            }
+        })
+        .await;
+
+    Ok(())
+}

src/tests/pre_messages/sending.rs

@@ -0,0 +1,337 @@
+//! Tests about sending pre-messages
+//! - When to send a pre-message and post-message instead of a normal message
+//! - Test that sent pre- and post-message contain the right Headers
+//!   and that they are send in the correct order (pre-message is sent first.)
+use anyhow::Result;
+use mailparse::MailHeaderMap;
+use tokio::fs;
+
+use crate::chat::{self, create_group, send_msg};
+use crate::config::Config;
+use crate::download::PRE_MSG_ATTACHMENT_SIZE_THRESHOLD;
+use crate::headerdef::{HeaderDef, HeaderDefMap};
+use crate::message::{Message, Viewtype};
+use crate::test_utils::{self, TestContext, TestContextManager};
+/// Tests that Pre-Message is sent for attachment larger than `PRE_MSG_ATTACHMENT_SIZE_THRESHOLD`
+/// Also test that Pre-Message is sent first, before the Post-Message
+/// And that Autocrypt-gossip and selfavatar never go into Post-Messages
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_sending_pre_message() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let fiona = &tcm.fiona().await;
+    let group_id = alice
+        .create_group_with_members("test group", &[bob, fiona])
+        .await;
+
+    let mut msg = Message::new(Viewtype::File);
+    msg.set_file_from_bytes(alice, "test.bin", &[0u8; 300_000], None)?;
+    msg.set_text("test".to_owned());
+
+    // assert that test attachment is bigger than limit
+    assert!(msg.get_filebytes(alice).await?.unwrap() > PRE_MSG_ATTACHMENT_SIZE_THRESHOLD);
+
+    let msg_id = chat::send_msg(alice, group_id, &mut msg).await?;
+    let smtp_rows = alice.get_smtp_rows_for_msg(msg_id).await;
+
+    //   Pre-Message and Post-Message should be present
+    //   and test that correct headers are present on both messages
+    assert_eq!(smtp_rows.len(), 2);
+    let pre_message = smtp_rows.first().expect("first element exists");
+    let pre_message_parsed = mailparse::parse_mail(pre_message.payload.as_bytes())?;
+    let post_message = smtp_rows.get(1).expect("second element exists");
+    let post_message_parsed = mailparse::parse_mail(post_message.payload.as_bytes())?;
+
+    assert!(
+        pre_message_parsed
+            .headers
+            .get_first_header(HeaderDef::ChatIsPostMessage.get_headername())
+            .is_none()
+    );
+    assert!(
+        post_message_parsed
+            .headers
+            .get_first_header(HeaderDef::ChatIsPostMessage.get_headername())
+            .is_some()
+    );
+
+    assert_eq!(
+        post_message_parsed
+            .headers
+            .get_header_value(HeaderDef::MessageId),
+        Some(format!("<{}>", msg.rfc724_mid)),
+        "Post-Message should have the rfc message id of the database message"
+    );
+
+    assert_ne!(
+        pre_message_parsed
+            .headers
+            .get_header_value(HeaderDef::MessageId),
+        post_message_parsed
+            .headers
+            .get_header_value(HeaderDef::MessageId),
+        "message ids of Pre-Message and Post-Message should be different"
+    );
+
+    let decrypted_post_message = bob.parse_msg(post_message).await;
+    assert_eq!(decrypted_post_message.decrypting_failed, false);
+    assert_eq!(
+        decrypted_post_message.header_exists(HeaderDef::ChatPostMessageId),
+        false
+    );
+
+    let decrypted_pre_message = bob.parse_msg(pre_message).await;
+    assert_eq!(
+        decrypted_pre_message
+            .get_header(HeaderDef::ChatPostMessageId)
+            .map(String::from),
+        post_message_parsed
+            .headers
+            .get_header_value(HeaderDef::MessageId)
+    );
+    assert!(
+        pre_message_parsed
+            .headers
+            .get_header_value(HeaderDef::ChatPostMessageId)
+            .is_none(),
+        "no Chat-Post-Message-ID header in unprotected headers of Pre-Message"
+    );
+
+    Ok(())
+}
+
+/// Tests that Pre-Message has autocrypt gossip headers and self avatar
+/// and Post-Message doesn't have these headers
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_selfavatar_and_autocrypt_gossip_goto_pre_message() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let fiona = &tcm.fiona().await;
+    let group_id = alice
+        .create_group_with_members("test group", &[bob, fiona])
+        .await;
+
+    let mut msg = Message::new(Viewtype::File);
+    msg.set_file_from_bytes(alice, "test.bin", &[0u8; 300_000], None)?;
+    msg.set_text("test".to_owned());
+
+    // assert that test attachment is bigger than limit
+    assert!(msg.get_filebytes(alice).await?.unwrap() > PRE_MSG_ATTACHMENT_SIZE_THRESHOLD);
+
+    // simulate conditions for sending self avatar
+    let avatar_src = alice.get_blobdir().join("avatar.png");
+    fs::write(&avatar_src, test_utils::AVATAR_900x900_BYTES).await?;
+    alice
+        .set_config(Config::Selfavatar, Some(avatar_src.to_str().unwrap()))
+        .await?;
+
+    let msg_id = chat::send_msg(alice, group_id, &mut msg).await?;
+    let smtp_rows = alice.get_smtp_rows_for_msg(msg_id).await;
+
+    assert_eq!(smtp_rows.len(), 2);
+    let pre_message = smtp_rows.first().expect("first element exists");
+    let post_message = smtp_rows.get(1).expect("second element exists");
+    let post_message_parsed = mailparse::parse_mail(post_message.payload.as_bytes())?;
+
+    let decrypted_pre_message = bob.parse_msg(pre_message).await;
+    assert!(
+        decrypted_pre_message
+            .get_header(HeaderDef::ChatPostMessageId)
+            .is_some(),
+        "tested message is not a pre-message, sending order may be broken"
+    );
+    assert_ne!(decrypted_pre_message.gossiped_keys.len(), 0);
+    assert_ne!(decrypted_pre_message.user_avatar, None);
+
+    let decrypted_post_message = bob.parse_msg(post_message).await;
+    assert!(
+        post_message_parsed
+            .headers
+            .get_first_header(HeaderDef::ChatIsPostMessage.get_headername())
+            .is_some(),
+        "tested message is not a Post-Message, sending order may be broken"
+    );
+    assert_eq!(decrypted_post_message.gossiped_keys.len(), 0);
+    assert_eq!(decrypted_post_message.user_avatar, None);
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_unecrypted_gets_no_pre_message() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+
+    let chat = alice
+        .create_chat_with_contact("example", "email@example.org")
+        .await;
+
+    let mut msg = Message::new(Viewtype::File);
+    msg.set_file_from_bytes(alice, "test.bin", &vec![0u8; 300_000], None)?;
+    msg.set_text("test".to_owned());
+
+    let msg_id = chat::send_msg(alice, chat.id, &mut msg).await?;
+    let smtp_rows = alice.get_smtp_rows_for_msg(msg_id).await;
+
+    assert_eq!(smtp_rows.len(), 1);
+    let message_bytes = smtp_rows
+        .first()
+        .expect("first element exists")
+        .payload
+        .as_bytes();
+    let message = mailparse::parse_mail(message_bytes)?;
+    assert!(
+        message
+            .headers
+            .get_first_header(HeaderDef::ChatIsPostMessage.get_headername())
+            .is_none(),
+    );
+    Ok(())
+}
+
+/// Tests that no pre message is sent for normal message
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_not_sending_pre_message_no_attachment() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let chat = alice.create_chat(bob).await;
+
+    // send normal text message
+    let mut msg = Message::new(Viewtype::Text);
+    msg.set_text("test".to_owned());
+    let msg_id = chat::send_msg(alice, chat.id, &mut msg).await.unwrap();
+    let smtp_rows = alice.get_smtp_rows_for_msg(msg_id).await;
+
+    assert_eq!(smtp_rows.len(), 1, "only one message should be sent");
+
+    let msg = smtp_rows.first().expect("first element exists");
+    let mail = mailparse::parse_mail(msg.payload.as_bytes())?;
+
+    assert!(
+        mail.headers
+            .get_first_header(HeaderDef::ChatIsPostMessage.get_headername())
+            .is_none(),
+        "no 'Chat-Is-Post-Message'-header should be present"
+    );
+    assert!(
+        mail.headers
+            .get_first_header(HeaderDef::ChatPostMessageId.get_headername())
+            .is_none(),
+        "no 'Chat-Post-Message-ID'-header should be present in clear text headers"
+    );
+    let decrypted_message = bob.parse_msg(msg).await;
+    assert!(
+        !decrypted_message.header_exists(HeaderDef::ChatPostMessageId),
+        "no 'Chat-Post-Message-ID'-header should be present"
+    );
+
+    // test that pre message is not send for large large text
+    let mut msg = Message::new(Viewtype::Text);
+    let long_text = String::from_utf8(vec![b'a'; 300_000])?;
+    assert!(long_text.len() > PRE_MSG_ATTACHMENT_SIZE_THRESHOLD.try_into().unwrap());
+    msg.set_text(long_text);
+    let msg_id = chat::send_msg(alice, chat.id, &mut msg).await.unwrap();
+    let smtp_rows = alice.get_smtp_rows_for_msg(msg_id).await;
+
+    assert_eq!(smtp_rows.len(), 1, "only one message should be sent");
+
+    let msg = smtp_rows.first().expect("first element exists");
+    let mail = mailparse::parse_mail(msg.payload.as_bytes())?;
+
+    assert!(
+        mail.headers
+            .get_first_header(HeaderDef::ChatIsPostMessage.get_headername())
+            .is_none()
+    );
+    assert!(
+        mail.headers
+            .get_first_header(HeaderDef::ChatPostMessageId.get_headername())
+            .is_none(),
+        "no 'Chat-Post-Message-ID'-header should be present in clear text headers"
+    );
+    let decrypted_message = bob.parse_msg(msg).await;
+    assert!(
+        !decrypted_message.header_exists(HeaderDef::ChatPostMessageId),
+        "no 'Chat-Post-Message-ID'-header should be present"
+    );
+    Ok(())
+}
+
+/// Tests that no pre message is sent for attachment smaller than `PRE_MSG_ATTACHMENT_SIZE_THRESHOLD`
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_not_sending_pre_message_for_small_attachment() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let chat = alice.create_chat(bob).await;
+
+    let mut msg = Message::new(Viewtype::File);
+    msg.set_file_from_bytes(alice, "test.bin", &vec![0u8; 100_000], None)?;
+    msg.set_text("test".to_owned());
+
+    // assert that test attachment is smaller than limit
+    assert!(msg.get_filebytes(alice).await?.unwrap() < PRE_MSG_ATTACHMENT_SIZE_THRESHOLD);
+
+    let msg_id = chat::send_msg(alice, chat.id, &mut msg).await.unwrap();
+    let smtp_rows = alice.get_smtp_rows_for_msg(msg_id).await;
+
+    //   only one message and no "is Post-Message" header should be present
+    assert_eq!(smtp_rows.len(), 1);
+
+    let msg = smtp_rows.first().expect("first element exists");
+    let mail = mailparse::parse_mail(msg.payload.as_bytes())?;
+
+    assert!(
+        mail.headers
+            .get_first_header(HeaderDef::ChatIsPostMessage.get_headername())
+            .is_none()
+    );
+    assert!(
+        mail.headers
+            .get_first_header(HeaderDef::ChatPostMessageId.get_headername())
+            .is_none(),
+        "no 'Chat-Post-Message-ID'-header should be present in clear text headers"
+    );
+    let decrypted_message = bob.parse_msg(msg).await;
+    assert!(
+        !decrypted_message.header_exists(HeaderDef::ChatPostMessageId),
+        "no 'Chat-Post-Message-ID'-header should be present"
+    );
+
+    Ok(())
+}
+
+/// Tests that pre message is not send for large webxdc updates
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_render_webxdc_status_update_object_range() -> Result<()> {
+    let t = TestContext::new_alice().await;
+    let chat_id = create_group(&t, "a chat").await?;
+
+    let instance = {
+        let mut instance = Message::new(Viewtype::File);
+        instance.set_file_from_bytes(
+            &t,
+            "minimal.xdc",
+            include_bytes!("../../../test-data/webxdc/minimal.xdc"),
+            None,
+        )?;
+        let instance_msg_id = send_msg(&t, chat_id, &mut instance).await?;
+        assert_eq!(instance.viewtype, Viewtype::Webxdc);
+        Message::load_from_db(&t, instance_msg_id).await
+    }
+    .unwrap();
+
+    t.pop_sent_msg().await;
+    assert_eq!(t.sql.count("SELECT COUNT(*) FROM smtp", ()).await?, 0);
+
+    let long_text = String::from_utf8(vec![b'a'; 300_000])?;
+    assert!(long_text.len() > PRE_MSG_ATTACHMENT_SIZE_THRESHOLD.try_into().unwrap());
+    t.send_webxdc_status_update(instance.id, &format!("{{\"payload\": \"{long_text}\"}}"))
+        .await?;
+    t.flush_status_updates().await?;
+
+    assert_eq!(t.sql.count("SELECT COUNT(*) FROM smtp", ()).await?, 1);
+    Ok(())
+}

src/tests/pre_messages/util.rs

@@ -0,0 +1,65 @@
+use anyhow::Result;
+use async_zip::tokio::write::ZipFileWriter;
+use async_zip::{Compression, ZipEntryBuilder};
+use futures::io::Cursor as FuturesCursor;
+use pretty_assertions::assert_eq;
+use tokio_util::compat::FuturesAsyncWriteCompatExt;
+
+use crate::chat::{self, ChatId};
+use crate::download::PRE_MSG_ATTACHMENT_SIZE_THRESHOLD;
+use crate::message::{Message, MsgId, Viewtype};
+use crate::test_utils::{SentMessage, TestContext, create_test_image};
+
+pub async fn send_large_file_message<'a>(
+    sender: &'a TestContext,
+    target_chat: ChatId,
+    view_type: Viewtype,
+    content: &[u8],
+) -> Result<(SentMessage<'a>, SentMessage<'a>, MsgId)> {
+    let mut msg = Message::new(view_type);
+    let file_name = if view_type == Viewtype::Webxdc {
+        "test.xdc"
+    } else {
+        "test.bin"
+    };
+    msg.set_file_from_bytes(sender, file_name, content, None)?;
+    msg.set_text("test".to_owned());
+
+    // assert that test attachment is bigger than limit
+    assert!(msg.get_filebytes(sender).await?.unwrap() > PRE_MSG_ATTACHMENT_SIZE_THRESHOLD);
+
+    let msg_id = chat::send_msg(sender, target_chat, &mut msg).await?;
+    let smtp_rows = sender.get_smtp_rows_for_msg(msg_id).await;
+
+    assert_eq!(smtp_rows.len(), 2);
+    let pre_message = smtp_rows.first().expect("Pre-Message exists");
+    let post_message = smtp_rows.get(1).expect("Post-Message exists");
+    Ok((pre_message.to_owned(), post_message.to_owned(), msg_id))
+}
+
+pub async fn send_large_webxdc_message<'a>(
+    sender: &'a TestContext,
+    target_chat: ChatId,
+) -> Result<(SentMessage<'a>, SentMessage<'a>, MsgId)> {
+    let futures_cursor = FuturesCursor::new(Vec::new());
+    let mut buffer = futures_cursor.compat_write();
+    let mut writer = ZipFileWriter::with_tokio(&mut buffer);
+    writer
+        .write_entry_whole(
+            ZipEntryBuilder::new("index.html".into(), Compression::Stored),
+            &[0u8; 1_000_000],
+        )
+        .await?;
+    writer.close().await?;
+    let big_webxdc_app = buffer.into_inner().into_inner();
+    send_large_file_message(sender, target_chat, Viewtype::Webxdc, &big_webxdc_app).await
+}
+
+pub async fn send_large_image_message<'a>(
+    sender: &'a TestContext,
+    target_chat: ChatId,
+) -> Result<(SentMessage<'a>, SentMessage<'a>, MsgId)> {
+    let (width, height) = (1080, 1920);
+    let test_img = create_test_image(width, height)?;
+    send_large_file_message(sender, target_chat, Viewtype::Image, &test_img).await
+}

src/webxdc/webxdc_tests.rs

@@ -10,9 +10,8 @@ use crate::chat::{
 };
 use crate::chatlist::Chatlist;
 use crate::config::Config;
-use crate::download::DownloadState;
 use crate::ephemeral;
-use crate::receive_imf::{receive_imf, receive_imf_from_inbox};
+use crate::receive_imf::receive_imf;
 use crate::test_utils::{E2EE_INFO_MSGS, TestContext, TestContextManager};
 use crate::tools::{self, SystemTime};
 use crate::{message, sql};
@@ -329,69 +328,6 @@ async fn test_webxdc_contact_request() -> Result<()> {
     Ok(())
 }
 
-#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn test_webxdc_update_for_not_downloaded_instance() -> Result<()> {
-    // Alice sends a larger instance and an update
-    let alice = TestContext::new_alice().await;
-    let bob = TestContext::new_bob().await;
-    let chat = alice.create_chat(&bob).await;
-    bob.set_config(Config::DownloadLimit, Some("40000")).await?;
-    let mut alice_instance = create_webxdc_instance(
-        &alice,
-        "chess.xdc",
-        include_bytes!("../../test-data/webxdc/chess.xdc"),
-    )?;
-    let sent1 = alice.send_msg(chat.id, &mut alice_instance).await;
-    let alice_instance = sent1.load_from_db().await;
-    alice
-        .send_webxdc_status_update(
-            alice_instance.id,
-            r#"{"payload": 7, "summary":"sum", "document":"doc"}"#,
-        )
-        .await?;
-    alice.flush_status_updates().await?;
-    let sent2 = alice.pop_sent_msg().await;
-
-    // Bob does not download instance but already receives update
-    receive_imf_from_inbox(
-        &bob,
-        &alice_instance.rfc724_mid,
-        sent1.payload().as_bytes(),
-        false,
-        Some(70790),
-    )
-    .await?;
-    let bob_instance = bob.get_last_msg().await;
-    bob_instance.chat_id.accept(&bob).await?;
-    bob.recv_msg_trash(&sent2).await;
-    assert_eq!(bob_instance.download_state, DownloadState::Available);
-
-    // Bob downloads instance, updates should be assigned correctly
-    let received_msg = receive_imf_from_inbox(
-        &bob,
-        &alice_instance.rfc724_mid,
-        sent1.payload().as_bytes(),
-        false,
-        None,
-    )
-    .await?
-    .unwrap();
-    assert_eq!(*received_msg.msg_ids.first().unwrap(), bob_instance.id);
-    let bob_instance = bob.get_last_msg().await;
-    assert_eq!(bob_instance.viewtype, Viewtype::Webxdc);
-    assert_eq!(bob_instance.download_state, DownloadState::Done);
-    assert_eq!(
-        bob.get_webxdc_status_updates(bob_instance.id, StatusUpdateSerial(0))
-            .await?,
-        r#"[{"payload":7,"document":"doc","summary":"sum","serial":1,"max_serial":1}]"#
-    );
-    let info = bob_instance.get_webxdc_info(&bob).await?;
-    assert_eq!(info.document, "doc");
-    assert_eq!(info.summary, "sum");
-
-    Ok(())
-}
-
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_delete_webxdc_instance() -> Result<()> {
     let t = TestContext::new_alice().await;