Make discussion mail References all notes in the discussiontc-correct-email-in-reply-to

When a note is part of a discussion, the email sent out will be
`In-Reply-To` the previous note in that discussion. It also
`References` all the previous notes in that discussion, and the
original issue.

Closes gitlab-org/gitlab-ce#36054.

1 files changed, 4 insertions, 4 deletions

diff --git a/app/mailers/notify.rb b/app/mailers/notify.rb
index 250583d2d28..ec886e993c3 100644
--- a/app/mailers/notify.rb
+++ b/app/mailers/notify.rb
@@ -119,8 +119,8 @@ class Notify < BaseMailer
       headers['Reply-To'] = address
 
       fallback_reply_message_id = "<reply-#{reply_key}@#{Gitlab.config.gitlab.host}>".freeze
-      headers['References'] ||= ''
-      headers['References'] << ' ' << fallback_reply_message_id
+      headers['References'] ||= []
+      headers['References'] << fallback_reply_message_id
 
       @reply_by_email = true
     end
@@ -158,8 +158,8 @@ class Notify < BaseMailer
 
   def mail_answer_note_thread(model, note, headers = {})
     headers['Message-ID'] = message_id(note)
-    headers['In-Reply-To'] = message_id(note.replies_to)
-    headers['References'] = message_id(model)
+    headers['In-Reply-To'] = message_id(note.references.last)
+    headers['References'] = note.references.map { |ref| message_id(ref) }
 
     headers['X-GitLab-Discussion-ID'] = note.discussion.id if note.part_of_discussion?