Sort message replies after parent message

src/dc_receive_imf.rs

@@ -698,6 +698,20 @@ async fn add_parts(
     let in_fresh = state == MessageState::InFresh;
     let rcvd_timestamp = time();
     let sort_timestamp = calc_sort_timestamp(context, *sent_timestamp, *chat_id, in_fresh).await;
+
+    // Ensure replies to messages are sorted after the parent message.
+    //
+    // This is useful in a case where sender clocks are not
+    // synchronized and parent message has a Date: header with a
+    // timestamp higher than reply timestamp.
+    //
+    // This does not help if parent message arrives later than the
+    // reply.
+    let parent_timestamp = mime_parser.get_parent_timestamp(context).await?;
+    let sort_timestamp = parent_timestamp.map_or(sort_timestamp, |parent_timestamp| {
+        std::cmp::max(sort_timestamp, parent_timestamp)
+    });
+
     *sent_timestamp = std::cmp::min(*sent_timestamp, rcvd_timestamp);
 
     // unarchive chat