Fix #2364. Fall back to In-Reply-To header when reply key not available

1 files changed, 15 insertions, 0 deletions

diff --git a/lib/gitlab/email/receiver.rb b/lib/gitlab/email/receiver.rb
index d4b6f6d120d..d55bacde5b0 100644
--- a/lib/gitlab/email/receiver.rb
+++ b/lib/gitlab/email/receiver.rb
@@ -63,6 +63,10 @@ module Gitlab
       end
 
       def reply_key
+        key_from_to_address || key_from_in_reply_to_header
+      end
+
+      def key_from_to_address
         key = nil
         message.to.each do |address|
           key = Gitlab::IncomingEmail.key_from_address(address)
@@ -72,6 +76,17 @@ module Gitlab
         key
       end
 
+      def key_from_in_reply_to_header
+        reply_key = nil
+
+        message[:in_reply_to].message_ids.each do |message_id|
+          reply_key = Gitlab::IncomingEmail.key_from_address(message_id)
+          break if reply_key
+        end
+
+        reply_key
+      end
+
       def sent_notification
         return nil unless reply_key