diff --git a/src/imap.rs b/src/imap.rs
index 896ee1c85..ca0d525e4 100644
--- a/src/imap.rs
+++ b/src/imap.rs
@@ -1282,6 +1282,7 @@ impl Session {
             return Ok(());
         }
         let is_chatmail = self.is_chatmail();
+        let transport_id = self.transport_id();
 
         for (request_uids, set) in build_sequence_sets(&request_uids)? {
             info!(context, "Starting UID FETCH of message set \"{}\".", set);
@@ -1381,17 +1382,7 @@ impl Session {
                 );
                 let res = receive_imf_inner(context, rfc724_mid, body, is_seen).await;
 
-                // If the message is not needed anymore on the server, mark it for deletion:
-                if !context.get_config_bool(Config::BccSelf).await? && is_chatmail {
-                    context
-                        .sql
-                        .execute(
-                            "UPDATE imap SET target='' WHERE rfc724_mid=?",
-                            (rfc724_mid,),
-                        )
-                        .await?;
-                    context.scheduler.interrupt_inbox().await;
-                }
+                maybe_mark_for_deletion(is_chatmail, transport_id, rfc724_mid, context).await?;
 
                 // If there was an error receiving the message, show a device message:
                 let received_msg = match res {
@@ -1664,6 +1655,26 @@ impl Session {
     }
 }
 
+async fn maybe_mark_for_deletion(
+    is_chatmail: bool,
+    transport_id: u32,
+    rfc724_mid: &String,
+    context: &Context,
+) -> Result<()> {
+    if !context.get_config_bool(Config::BccSelf).await? && is_chatmail {
+        context
+            .sql
+            .execute(
+                "UPDATE imap SET target='' WHERE rfc724_mid=? AND transport_id=?",
+                (rfc724_mid, transport_id),
+            )
+            .await?;
+        context.scheduler.interrupt_inbox().await;
+    }
+
+    Ok(())
+}
+
 fn format_setmetadata(folder: &str, device_token: &str) -> String {
     let device_token_len = device_token.len();
     format!(
@@ -1972,6 +1983,15 @@ pub(crate) fn create_message_id() -> String {
 }
 
 /// Determines whether the message should be downloaded based on prefetched headers.
+// We want to call maybe_delete() iff it's not a post-message OR the post-message was already downloaded.
+// I.e. if it's a post-message that is Available, Failure, or InProgress, then we do not want to delete it.
+// WRT InProgress, we do want to delete it later on _all_ relays later, after we downloaded it.
+// So, maybe when choosing what to delete, we should not filter by transport.
+// I'm not sure about checking is_chatmail - maybe it's fine to just remove a message from all transports
+// if it also arrived via a chatmail transport,
+// because generally the only reason why this happens is because the chatpartner has DC with multi-relay.
+//
+// I.e., we want to delete everything for which prefetch_should_download() returns false, EXCEPT for the case where a post-message's download failed or is in progress.
 pub(crate) async fn prefetch_should_download(
     context: &Context,
     headers: &[mailparse::MailHeader<'_>],
diff --git a/src/message.rs b/src/message.rs
index b2be0169d..90ec049b7 100644
--- a/src/message.rs
+++ b/src/message.rs
@@ -2220,6 +2220,36 @@ pub(crate) async fn rfc724_mid_download_tried(context: &Context, rfc724_mid: &st
     Ok(res)
 }
 
+/// Returns `true` iff there is a message
+/// with the given `rfc724_mid`
+/// and a download state other than `DownloadState::Available`,
+/// i.e. it was already tried to download the message or it's sent locally.
+pub(crate) async fn rfc724_mid_was_downloaded(context: &Context, rfc724_mid: &str) -> Result<bool> {
+    let rfc724_mid = rfc724_mid.trim_start_matches('<').trim_end_matches('>');
+    if rfc724_mid.is_empty() {
+        warn!(
+            context,
+            "Empty rfc724_mid passed to rfc724_mid_download_tried"
+        );
+        return Ok(false);
+    }
+
+    let res = context
+        .sql
+        .exists(
+            "SELECT COUNT(*) FROM msgs
+             WHERE rfc724_mid=? AND download_state=? OR download_state=?",
+            (
+                rfc724_mid,
+                DownloadState::Done,
+                DownloadState::Undecipherable,
+            ),
+        )
+        .await?;
+
+    Ok(res)
+}
+
 /// Given a list of Message-IDs, returns the most relevant message found in the database.
 ///
 /// Relevance here is `(download_state == Done, index)`, where `index` is an index of Message-ID in