fix: Fail receive_imf to not tombstone self-MDN if original message isn't found

This way if the self-MDN isn't applied successfully, it can be received again and retried.

.github/workflows/ci.yml

@@ -41,9 +41,6 @@ jobs:
         shell: bash
       - name: Cache rust cargo artifacts
         uses: swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4
-        with:
-          save-if: false
-          add-rust-environment-hash-key: false
       - name: Run rustfmt
         run: cargo fmt --all -- --check
       - name: Run clippy
@@ -93,15 +90,8 @@ jobs:
         with:
           show-progress: false
           persist-credentials: false
-
-      - run: rustup override set $RUST_VERSION
-        shell: bash
-
       - name: Cache rust cargo artifacts
         uses: swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4
-        with:
-          save-if: false
-          add-rust-environment-hash-key: false
       - name: Rustdoc
         run: cargo doc --document-private-items --no-deps
 
@@ -145,15 +135,6 @@ jobs:
 
       - name: Cache rust cargo artifacts
         uses: swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4
-        with:
-          # Only save the cache from the main branch runs.
-          # No need for PRs to write to the cache.
-          ##save-if: ${{ github.ref == 'refs/heads/main' }}
-
-          # Do not hash Cargo.lock.
-          # We want the cache to be used later in PRs
-          # even if it updates some dependency.
-          add-rust-environment-hash-key: false
 
       - name: Install nextest
         uses: taiki-e/install-action@5f57d6cb7cd20b14a8a27f522884c4bc8a187458
@@ -186,14 +167,8 @@ jobs:
           show-progress: false
           persist-credentials: false
 
-      - run: rustup override set $RUST_VERSION
-        shell: bash
-
       - name: Cache rust cargo artifacts
         uses: swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4
-        with:
-          save-if: false
-          add-rust-environment-hash-key: false
 
       - name: Build C library
         run: cargo build -p deltachat_ffi
@@ -218,14 +193,8 @@ jobs:
           show-progress: false
           persist-credentials: false
 
-      - run: rustup override set $RUST_VERSION
-        shell: bash
-
       - name: Cache rust cargo artifacts
         uses: swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4
-        with:
-          save-if: false
-          add-rust-environment-hash-key: false
 
       - name: Build deltachat-rpc-server
         run: cargo build -p deltachat-rpc-server

Cargo.lock

@@ -36,7 +36,7 @@ checksum = "b169f7a6d4742236a0a00c541b845991d0ac43e546831af1249753ab4c3aa3a0"
 dependencies = [
  "cfg-if",
  "cipher",
- "cpufeatures 0.2.17",
+ "cpufeatures",
 ]
 
 [[package]]
@@ -136,7 +136,7 @@ checksum = "3c3610892ee6e0cbce8ae2700349fcf8f98adb0dbfbee85aec3c9179d29cc072"
 dependencies = [
  "base64ct",
  "blake2",
- "cpufeatures 0.2.17",
+ "cpufeatures",
  "password-hash",
  "zeroize",
 ]
@@ -497,16 +497,16 @@ dependencies = [
 
 [[package]]
 name = "blake3"
-version = "1.8.5"
+version = "1.8.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0aa83c34e62843d924f905e0f5c866eb1dd6545fc4d719e803d9ba6030371fce"
+checksum = "2468ef7d57b3fb7e16b576e8377cdbde2320c60e1491e961d11da40fc4f02a2d"
 dependencies = [
  "arrayref",
  "arrayvec",
  "cc",
  "cfg-if",
  "constant_time_eq 0.4.2",
- "cpufeatures 0.3.0",
+ "cpufeatures",
 ]
 
 [[package]]
@@ -799,7 +799,7 @@ checksum = "c3613f74bd2eac03dad61bd53dbe620703d4371614fe0bc3b9f04dd36fe4e818"
 dependencies = [
  "cfg-if",
  "cipher",
- "cpufeatures 0.2.17",
+ "cpufeatures",
 ]
 
 [[package]]
@@ -1011,15 +1011,6 @@ dependencies = [
  "libc",
 ]
 
-[[package]]
-name = "cpufeatures"
-version = "0.3.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8b2a41393f66f16b0823bb79094d54ac5fbd34ab292ddafb9a0456ac9f87d201"
-dependencies = [
- "libc",
-]
-
 [[package]]
 name = "crc"
 version = "3.2.1"
@@ -1225,7 +1216,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "97fb8b7c4503de7d6ae7b42ab72a5a59857b4c937ec27a3d4539dba95b5ab2be"
 dependencies = [
  "cfg-if",
- "cpufeatures 0.2.17",
+ "cpufeatures",
  "curve25519-dalek-derive",
  "digest",
  "fiat-crypto",
@@ -3255,7 +3246,7 @@ version = "0.1.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cb26cec98cce3a3d96cbb7bced3c4b16e3d13f27ec56dbd62cbc8f39cfb9d653"
 dependencies = [
- "cpufeatures 0.2.17",
+ "cpufeatures",
 ]
 
 [[package]]
@@ -4421,7 +4412,7 @@ version = "0.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8159bd90725d2df49889a078b54f4f79e87f1f8a8444194cdca81d38f5393abf"
 dependencies = [
- "cpufeatures 0.2.17",
+ "cpufeatures",
  "opaque-debug",
  "universal-hash",
 ]
@@ -4433,7 +4424,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9d1fe60d06143b2430aa532c94cfe9e29783047f06c0d7fd359a9a51b729fa25"
 dependencies = [
  "cfg-if",
- "cpufeatures 0.2.17",
+ "cpufeatures",
  "opaque-debug",
  "universal-hash",
 ]
@@ -5517,7 +5508,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f5058ada175748e33390e40e872bd0fe59a19f265d0158daa551c5a88a76009c"
 dependencies = [
  "cfg-if",
- "cpufeatures 0.2.17",
+ "cpufeatures",
  "digest",
 ]
 
@@ -5528,7 +5519,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e3bf829a2d51ab4a5ddf1352d8470c140cadc8301b2ae1789db023f01cedd6ba"
 dependencies = [
  "cfg-if",
- "cpufeatures 0.2.17",
+ "cpufeatures",
  "digest",
 ]
 
@@ -5556,7 +5547,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a7507d819769d01a365ab707794a4084392c824f54a7a6a7862f8c3d0892b283"
 dependencies = [
  "cfg-if",
- "cpufeatures 0.2.17",
+ "cpufeatures",
  "digest",
 ]
 

deltachat-rpc-client/tests/test_something.py

@@ -348,7 +348,7 @@ def test_receive_imf_failure(acfactory) -> None:
         snapshot.text == "❌ Failed to receive a message:"
         " Condition failed: `!context.get_config_bool(Config::SimulateReceiveImfError).await?`."
         f" Core version {version}."
-        " Please report this bug to delta@merlinux.eu or https://support.delta.chat/."
+        " Please report this bug to delta@merlinux.eu or https://support.delta.chat/"
     )
 
     # The failed message doesn't break the IMAP loop.

deny.toml

@@ -33,17 +33,7 @@ ignore = [
     # We do not check CRL and cannot update rustls-webpki 0.102.8 
     # which is a dependency of iroh 0.35.0.
     # <https://rustsec.org/advisories/RUSTSEC-2026-0104>
-    "RUSTSEC-2026-0104",
-
-    # hickory-proto 0.25.2 unbounded loop in DNSSEC code.
-    # Dependency of iroh 0.35.0, cannot be updated as of 2026-05-02.
-    # <https://rustsec.org/advisories/RUSTSEC-2026-0118>
-    "RUSTSEC-2026-0118",
-
-    # hickory-proto 0.25.2 quadratic complexity issue.
-    # Dependency of iroh 0.35.0, cannot be updated as of 2026-05-02.
-    # <https://rustsec.org/advisories/RUSTSEC-2026-0119>
-    "RUSTSEC-2026-0119"
+    "RUSTSEC-2026-0104"
 ]
 
 [bans]

src/imap.rs

@@ -1383,13 +1383,15 @@ impl Session {
                 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:#}.");
-
-                        let text = format!(
-                            "❌ Failed to receive a message: {err:#}. Core version v{DC_VERSION_STR}. Please report this bug to delta@merlinux.eu or https://support.delta.chat/.",
-                        );
-                        let mut msg = Message::new_text(text);
-                        add_device_msg(context, None, Some(&mut msg)).await?;
+                        let err = format!("{err:#}");
+                        warn!(context, "receive_imf error: {err}.");
+                        if !err.contains("(SKIP_DEVICE_MSG)") {
+                            let text = format!(
+                                "❌ Failed to receive a message: {err}. Core version v{DC_VERSION_STR}. Please report this bug to delta@merlinux.eu or https://support.delta.chat/",
+                            );
+                            let mut msg = Message::new_text(text);
+                            add_device_msg(context, None, Some(&mut msg)).await?;
+                        }
                         None
                     }
                     Ok(msg) => msg,

src/reaction.rs

@@ -18,7 +18,7 @@ use std::cmp::Ordering;
 use std::collections::BTreeMap;
 use std::fmt;
 
-use anyhow::Result;
+use anyhow::{Result, bail};
 use serde::{Deserialize, Serialize};
 
 use crate::chat::{Chat, ChatId, send_msg};
@@ -259,9 +259,8 @@ pub(crate) async fn set_msg_reaction(
             });
         }
     } else {
-        info!(
-            context,
-            "Can't assign reaction to unknown message with Message-ID {}", in_reply_to
+        bail!(
+            "Can't assign reaction to unknown message with Message-ID {in_reply_to} (SKIP_DEVICE_MSG)"
         );
     }
     Ok(())
@@ -519,6 +518,54 @@ Content-Disposition: reaction\n\
         Ok(())
     }
 
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_reaction_and_multitransport() -> Result<()> {
+        let mut tcm = TestContextManager::new();
+        let alice = &tcm.alice().await;
+        let device_chat_id = ChatId::get_for_contact(alice, ContactId::DEVICE).await?;
+        let n_device_msgs = get_chat_msgs(alice, device_chat_id).await?.len();
+
+        let reaction_bytes = "To: alice@example.org, claire@example.org\n\
+From: bob@example.net\n\
+Date: Today, 29 February 2021 00:00:10 -800\n\
+Message-ID: 56789@example.net\n\
+In-Reply-To: 12345@example.org\n\
+Content-Type: text/plain; charset=utf-8\n\
+Content-Disposition: reaction\n\
+\n\
+\u{1F44D}"
+            .as_bytes();
+        // Alice receives a reaction to Claire's message from Bob earler than the message itself
+        // because Bob knows about Alice's new transport.
+        assert!(receive_imf(alice, reaction_bytes, false).await.is_err());
+
+        let msg_id = receive_imf(
+            alice,
+            "To: alice@example.org, bob@example.net\n\
+From: claire@example.org\n\
+Date: Today, 29 February 2021 00:00:00 -800\n\
+Message-ID: 12345@example.org\n\
+\n\
+Can we chat at 1pm pacific, today?"
+                .as_bytes(),
+            false,
+        )
+        .await?
+        .unwrap()
+        .msg_ids[0];
+
+        // Finally the reaction arrives on Alice's older transport.
+        receive_imf(alice, reaction_bytes, false).await?;
+        let reactions = get_msg_reactions(alice, msg_id).await?;
+        assert_eq!(reactions.to_string(), "👍1");
+
+        assert_eq!(
+            get_chat_msgs(alice, device_chat_id).await?.len(),
+            n_device_msgs
+        );
+        Ok(())
+    }
+
     async fn expect_reactions_changed_event(
         t: &TestContext,
         expected_chat_id: ChatId,

src/receive_imf.rs

@@ -6,7 +6,7 @@ use std::iter;
 use std::str::FromStr as _;
 use std::sync::LazyLock;
 
-use anyhow::{Context as _, Result, ensure};
+use anyhow::{Context as _, Result, bail, ensure};
 use deltachat_contact_tools::{
     ContactAddress, addr_cmp, addr_normalize, may_be_valid_addr, sanitize_bidi_characters,
     sanitize_single_line,
@@ -935,75 +935,6 @@ UPDATE config SET value=? WHERE keyname='configured_addr' AND value!=?1
             // This is a Delta Chat MDN. Mark as read.
             markseen_on_imap_table(context, rfc724_mid_orig).await?;
         }
-        if !mime_parser.incoming && !context.get_config_bool(Config::TeamProfile).await? {
-            let mut updated_chats = BTreeMap::new();
-            let mut archived_chats_maybe_noticed = false;
-            for report in &mime_parser.mdn_reports {
-                for msg_rfc724_mid in report
-                    .original_message_id
-                    .iter()
-                    .chain(&report.additional_message_ids)
-                {
-                    let Some(msg_id) = rfc724_mid_exists(context, msg_rfc724_mid).await? else {
-                        continue;
-                    };
-                    let Some(msg) = Message::load_from_db_optional(context, msg_id).await? else {
-                        continue;
-                    };
-                    if msg.state < MessageState::InFresh || msg.state >= MessageState::InSeen {
-                        continue;
-                    }
-                    if !mime_parser.was_encrypted() && msg.get_showpadlock() {
-                        warn!(context, "MDN: Not encrypted. Ignoring.");
-                        continue;
-                    }
-                    message::update_msg_state(context, msg_id, MessageState::InSeen).await?;
-                    if let Err(e) = msg_id.start_ephemeral_timer(context).await {
-                        error!(context, "start_ephemeral_timer for {msg_id}: {e:#}.");
-                    }
-                    if !mime_parser.has_chat_version() {
-                        continue;
-                    }
-                    archived_chats_maybe_noticed |= msg.state < MessageState::InNoticed
-                        && msg.chat_visibility == ChatVisibility::Archived;
-                    updated_chats
-                        .entry(msg.chat_id)
-                        .and_modify(|pos| *pos = cmp::max(*pos, (msg.timestamp_sort, msg.id)))
-                        .or_insert((msg.timestamp_sort, msg.id));
-                }
-            }
-            for (chat_id, (timestamp_sort, msg_id)) in updated_chats {
-                context
-                    .sql
-                    .execute(
-                        "
-UPDATE msgs SET state=? WHERE
-    state=? AND
-    hidden=0 AND
-    chat_id=? AND
-    (timestamp,id)<(?,?)",
-                        (
-                            MessageState::InNoticed,
-                            MessageState::InFresh,
-                            chat_id,
-                            timestamp_sort,
-                            msg_id,
-                        ),
-                    )
-                    .await
-                    .context("UPDATE msgs.state")?;
-                if chat_id.get_fresh_msg_cnt(context).await? == 0 {
-                    // Removes all notifications for the chat in UIs.
-                    context.emit_event(EventType::MsgsNoticed(chat_id));
-                } else {
-                    context.emit_msgs_changed_without_msg_id(chat_id);
-                }
-                chatlist_events::emit_chatlist_item_changed(context, chat_id);
-            }
-            if archived_chats_maybe_noticed {
-                context.on_archived_chats_maybe_noticed();
-            }
-        }
     }
 
     if mime_parser.is_call() {
@@ -2065,9 +1996,8 @@ async fn add_parts(
                     }
                 }
                 None => {
-                    warn!(
-                        context,
-                        "Cannot add iroh peer because WebXDC instance does not exist."
+                    bail!(
+                        "Cannot add iroh peer because WebXDC instance {in_reply_to} does not exist (SKIP_DEVICE_MSG)"
                     );
                 }
             },
@@ -2100,6 +2030,82 @@ async fn add_parts(
             warn!(context, "Call: Not a reply.")
         }
     }
+    if !mime_parser.incoming && !context.get_config_bool(Config::TeamProfile).await? {
+        let mut missing_rfc724_mid = None;
+        let mut updated_chats = BTreeMap::new();
+        let mut archived_chats_maybe_noticed = false;
+        for report in &mime_parser.mdn_reports {
+            for msg_rfc724_mid in report
+                .original_message_id
+                .iter()
+                .chain(&report.additional_message_ids)
+            {
+                let Some(msg_id) = rfc724_mid_exists(context, msg_rfc724_mid).await? else {
+                    missing_rfc724_mid.get_or_insert(msg_rfc724_mid.as_str());
+                    continue;
+                };
+                let Some(msg) = Message::load_from_db_optional(context, msg_id).await? else {
+                    continue;
+                };
+                if msg.state < MessageState::InFresh || msg.state >= MessageState::InSeen {
+                    continue;
+                }
+                if !mime_parser.was_encrypted() && msg.get_showpadlock() {
+                    warn!(context, "MDN: Not encrypted. Ignoring.");
+                    continue;
+                }
+                message::update_msg_state(context, msg_id, MessageState::InSeen).await?;
+                if let Err(e) = msg_id.start_ephemeral_timer(context).await {
+                    error!(context, "start_ephemeral_timer for {msg_id}: {e:#}.");
+                }
+                if !mime_parser.has_chat_version() {
+                    continue;
+                }
+                archived_chats_maybe_noticed |= msg.state < MessageState::InNoticed
+                    && msg.chat_visibility == ChatVisibility::Archived;
+                updated_chats
+                    .entry(msg.chat_id)
+                    .and_modify(|pos| *pos = cmp::max(*pos, (msg.timestamp_sort, msg.id)))
+                    .or_insert((msg.timestamp_sort, msg.id));
+            }
+        }
+        for (chat_id, (timestamp_sort, msg_id)) in updated_chats {
+            context
+                .sql
+                .execute(
+                    "
+UPDATE msgs SET state=? WHERE
+state=? AND
+hidden=0 AND
+chat_id=? AND
+(timestamp,id)<(?,?)",
+                    (
+                        MessageState::InNoticed,
+                        MessageState::InFresh,
+                        chat_id,
+                        timestamp_sort,
+                        msg_id,
+                    ),
+                )
+                .await
+                .context("UPDATE msgs.state")?;
+            if chat_id.get_fresh_msg_cnt(context).await? == 0 {
+                // Removes all notifications for the chat in UIs.
+                context.emit_event(EventType::MsgsNoticed(chat_id));
+            } else {
+                context.emit_msgs_changed_without_msg_id(chat_id);
+            }
+            chatlist_events::emit_chatlist_item_changed(context, chat_id);
+        }
+        if archived_chats_maybe_noticed {
+            context.on_archived_chats_maybe_noticed();
+        }
+        ensure!(
+            missing_rfc724_mid.is_none(),
+            "Self-MDN: {} not found (SKIP_DEVICE_MSG)",
+            missing_rfc724_mid.unwrap_or(""),
+        );
+    }
 
     let hidden = mime_parser.parts.iter().all(|part| part.is_reaction);
     let mut parts = mime_parser.parts.iter().peekable();
@@ -2380,10 +2386,7 @@ async fn handle_edit_delete(
                 warn!(context, "Edit message: Database entry does not exist.");
             }
         } else {
-            warn!(
-                context,
-                "Edit message: rfc724_mid {rfc724_mid:?} not found."
-            );
+            bail!("Edit message: rfc724_mid {rfc724_mid:?} not found (SKIP_DEVICE_MSG)");
         }
     } else if let Some(rfc724_mid_list) = mime_parser.get_header(HeaderDef::ChatDelete)
         && let Some(part) = mime_parser.parts.first()

src/receive_imf/receive_imf_tests.rs

@@ -14,7 +14,9 @@ use crate::contact;
 use crate::imap::prefetch_should_download;
 use crate::imex::{ImexMode, imex};
 use crate::key;
+use crate::message::markseen_msgs;
 use crate::securejoin::get_securejoin_qr;
+use crate::smtp;
 use crate::test_utils::{
     TestContext, TestContextManager, alice_keypair, get_chat_msg, mark_as_verified,
 };
@@ -2655,6 +2657,32 @@ async fn test_read_receipts_dont_unmark_bots() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_self_mdn_before_msg() -> Result<()> {
+    let mut tcm = TestContextManager::new();
+    let alice = &tcm.alice().await;
+    let bob = &tcm.bob().await;
+    let bob2 = &tcm.bob().await;
+    let alice_chat = alice.create_chat(bob).await;
+
+    let sent = alice.send_text(alice_chat.id, "hi").await;
+    let msg = bob.recv_msg(&sent).await;
+    msg.chat_id.accept(bob).await?;
+    markseen_msgs(bob, vec![msg.id]).await?;
+    smtp::queue_mdn(bob).await?;
+    let sent_mdn = bob.pop_sent_msg().await;
+
+    let Err(err) = receive_imf(bob2, sent_mdn.payload().as_bytes(), false).await else {
+        unreachable!();
+    };
+    assert!(format!("{err:#}").contains("(SKIP_DEVICE_MSG)"));
+    let msg = bob2.recv_msg(&sent).await;
+    assert_eq!(msg.get_state(), MessageState::InFresh);
+    bob2.recv_msg_trash(&sent_mdn).await;
+    assert_eq!(msg.id.get_state(bob2).await?, MessageState::InSeen);
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_gmx_forwarded_msg() -> Result<()> {
     let t = TestContext::new_alice().await;

src/smtp.rs

@@ -13,7 +13,7 @@ use crate::config::Config;
 use crate::contact::{Contact, ContactId};
 use crate::context::Context;
 use crate::events::EventType;
-use crate::log::{LogExt, warn};
+use crate::log::warn;
 use crate::message::Message;
 use crate::message::{self, MsgId};
 use crate::mimefactory::MimeFactory;
@@ -590,44 +590,77 @@ async fn send_mdn_rfc724_mid(
     if context.get_config_bool(Config::BccSelf).await? {
         add_self_recipients(context, &mut recipients, encrypted).await?;
     }
-    let recipients: Vec<_> = recipients
-        .into_iter()
-        .filter_map(|addr| {
-            async_smtp::EmailAddress::new(addr.clone())
-                .with_context(|| format!("Invalid recipient: {addr}"))
-                .log_err(context)
-                .ok()
-        })
-        .collect();
+    #[cfg(not(test))]
+    {
+        use crate::log::LogExt;
 
-    match smtp_send(context, &recipients, &body, smtp, None).await {
-        SendResult::Success => {
-            if !recipients.is_empty() {
-                info!(context, "Successfully sent MDN for {rfc724_mid}.");
+        let recipients: Vec<_> = recipients
+            .into_iter()
+            .filter_map(|addr| {
+                async_smtp::EmailAddress::new(addr.clone())
+                    .with_context(|| format!("Invalid recipient: {addr}"))
+                    .log_err(context)
+                    .ok()
+            })
+            .collect();
+
+        match smtp_send(context, &recipients, &body, smtp, None).await {
+            SendResult::Success => {
+                if !recipients.is_empty() {
+                    info!(context, "Successfully sent MDN for {rfc724_mid}.");
+                }
+                context
+                    .sql
+                    .transaction(|transaction| {
+                        let mut stmt =
+                            transaction.prepare("DELETE FROM smtp_mdns WHERE rfc724_mid = ?")?;
+                        stmt.execute((rfc724_mid,))?;
+                        for additional_rfc724_mid in additional_rfc724_mids {
+                            stmt.execute((additional_rfc724_mid,))?;
+                        }
+                        Ok(())
+                    })
+                    .await?;
+                Ok(true)
             }
-            context
-                .sql
-                .transaction(|transaction| {
-                    let mut stmt =
-                        transaction.prepare("DELETE FROM smtp_mdns WHERE rfc724_mid = ?")?;
-                    stmt.execute((rfc724_mid,))?;
-                    for additional_rfc724_mid in additional_rfc724_mids {
-                        stmt.execute((additional_rfc724_mid,))?;
-                    }
-                    Ok(())
-                })
-                .await?;
-            Ok(true)
+            SendResult::Retry => {
+                info!(
+                    context,
+                    "Temporary SMTP failure while sending an MDN for {rfc724_mid}."
+                );
+                Ok(false)
+            }
+            SendResult::Failure(err) => Err(err),
         }
-        SendResult::Retry => {
-            info!(
-                context,
-                "Temporary SMTP failure while sending an MDN for {rfc724_mid}."
-            );
-            Ok(false)
-        }
-        SendResult::Failure(err) => Err(err),
     }
+    #[cfg(test)]
+    {
+        let _ = smtp;
+        context
+            .sql
+            .transaction(|t| {
+                t.execute(
+                    "INSERT INTO smtp (rfc724_mid, recipients, mime, msg_id)
+                    VALUES (?, ?, ?, ?)",
+                    (rfc724_mid, recipients.join(" "), body, u32::MAX),
+                )?;
+                let mut stmt = t.prepare("DELETE FROM smtp_mdns WHERE rfc724_mid = ?")?;
+                stmt.execute((rfc724_mid,))?;
+                for additional_rfc724_mid in additional_rfc724_mids {
+                    stmt.execute((additional_rfc724_mid,))?;
+                }
+                Ok(())
+            })
+            .await?;
+        Ok(true)
+    }
+}
+
+#[cfg(test)]
+pub(crate) async fn queue_mdn(context: &Context) -> Result<()> {
+    let queued = send_mdn(context, &mut Smtp::new()).await?;
+    assert!(queued);
+    Ok(())
 }
 
 /// Tries to send a single MDN. Returns true if more MDNs should be sent.