fix: Treat only "Auto-Submitted: auto-generated" messages as bot-sent (#5213)

"Auto-Submitted: auto-replied" messages mustn't be considered as sent by either bots or non-bots,
e.g. MDNs have this header value and it's the same for bots and non-bots.

src/message.rs

@@ -757,7 +757,7 @@ impl Message {
         self.param.get_int(Param::GuaranteeE2ee).unwrap_or_default() != 0
     }
 
-    /// Returns true if message is Auto-Submitted.
+    /// Returns true if message is auto-generated.
     pub fn is_bot(&self) -> bool {
         self.param.get_bool(Param::Bot).unwrap_or_default()
     }

src/mimeparser.rs

@@ -117,8 +117,8 @@ pub(crate) struct MimeMessage {
     /// Hop info for debugging.
     pub(crate) hop_info: String,
 
-    /// Whether the contact sending this should be marked as bot.
+    /// Whether the contact sending this should be marked as bot or non-bot.
-    pub(crate) is_bot: bool,
+    pub(crate) is_bot: Option<bool>,
 
     /// When the message was received, in secs since epoch.
     pub(crate) timestamp_rcvd: i64,
@@ -394,9 +394,6 @@ impl MimeMessage {
             }
         }
 
-        // Auto-submitted is also set by holiday-notices so we also check `chat-version`
-        let is_bot = headers.contains_key("auto-submitted") && headers.contains_key("chat-version");
-
         let timestamp_rcvd = smeared_time(context);
         let timestamp_sent = headers
             .get(HeaderDef::Date.get_headername())
@@ -431,7 +428,7 @@ impl MimeMessage {
             is_mime_modified: false,
             decoded_data: Vec::new(),
             hop_info,
-            is_bot,
+            is_bot: None,
             timestamp_rcvd,
             timestamp_sent,
         };
@@ -464,6 +461,13 @@ impl MimeMessage {
             },
         };
 
+        if parser.mdn_reports.is_empty() {
+            // "Auto-Submitted" is also set by holiday-notices so we also check "chat-version".
+            let is_bot = parser.headers.get("auto-submitted")
+                == Some(&"auto-generated".to_string())
+                && parser.headers.contains_key("chat-version");
+            parser.is_bot = Some(is_bot);
+        }
         parser.maybe_remove_bad_parts();
         parser.maybe_remove_inline_mailinglist_footer();
         parser.heuristically_parse_ndn(context).await;
@@ -702,7 +706,7 @@ impl MimeMessage {
             self.do_add_single_part(part);
         }
 
-        if self.headers.contains_key("auto-submitted") {
+        if self.is_bot == Some(true) {
             for part in &mut self.parts {
                 part.param.set(Param::Bot, "1");
             }
@@ -2740,6 +2744,7 @@ Chat-Version: 1.0\n\
 Message-ID: <bar@example.org>\n\
 To: Alice <alice@example.org>\n\
 From: Bob <bob@example.org>\n\
+Auto-Submitted: auto-replied\n\
 Content-Type: multipart/report; report-type=disposition-notification;\n\t\
 boundary=\"kJBbU58X1xeWNHgBtTbMk80M5qnV4N\"\n\
 \n\
@@ -2775,6 +2780,7 @@ Disposition: manual-action/MDN-sent-automatically; displayed\n\
 
         assert_eq!(message.parts.len(), 1);
         assert_eq!(message.mdn_reports.len(), 1);
+        assert_eq!(message.is_bot, None);
     }
 
     /// Test parsing multiple MDNs combined in a single message.

src/param.rs

@@ -65,7 +65,7 @@ pub enum Param {
     /// For Messages: the message is a reaction.
     Reaction = b'x',
 
-    /// For Messages: a message with Auto-Submitted header ("bot").
+    /// For Messages: a message with "Auto-Submitted: auto-generated" header ("bot").
     Bot = b'b',
 
     /// For Messages: unset or 0=not forwarded,

src/receive_imf.rs

@@ -539,7 +539,9 @@ pub(crate) async fn receive_imf_inner(
         .handle_reports(context, from_id, &mime_parser.parts)
         .await;
 
-    from_id.mark_bot(context, mime_parser.is_bot).await?;
+    if let Some(is_bot) = mime_parser.is_bot {
+        from_id.mark_bot(context, is_bot).await?;
+    }
 
     Ok(Some(received_msg))
 }

src/receive_imf/tests.rs

@@ -2684,6 +2684,36 @@ async fn test_read_receipts_dont_create_chats() -> Result<()> {
     Ok(())
 }
 
+/// Test that read receipts don't unmark contacts as bots.
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn test_read_receipts_dont_unmark_bots() -> Result<()> {
+    let alice = &TestContext::new_alice().await;
+    let bob = &TestContext::new_bob().await;
+    let ab_contact = alice.add_or_lookup_contact(bob).await;
+    ab_contact.id.mark_bot(alice, true).await?;
+    let alice_chat = alice.create_chat(bob).await;
+
+    // Alice sends and Bob receives a message.
+    bob.recv_msg(&alice.send_text(alice_chat.id, "Message").await)
+        .await;
+    let received_msg = bob.get_last_msg().await;
+
+    // Bob sends a read receipt.
+    let mdn_mimefactory =
+        crate::mimefactory::MimeFactory::from_mdn(bob, &received_msg, vec![]).await?;
+    let rendered_mdn = mdn_mimefactory.render(bob).await?;
+    let mdn_body = rendered_mdn.message;
+
+    // Alice receives the read receipt.
+    receive_imf(alice, mdn_body.as_bytes(), false).await?;
+    let msg = alice.get_last_msg_in(alice_chat.id).await;
+    assert_eq!(msg.state, MessageState::OutMdnRcvd);
+    let ab_contact = alice.add_or_lookup_contact(bob).await;
+    assert!(ab_contact.is_bot());
+
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_gmx_forwarded_msg() -> Result<()> {
     let t = TestContext::new_alice().await;