<p><b>@tomhughes</b> commented on this pull request.</p>

<hr>

<p>In <a href="https://github.com/openstreetmap/openstreetmap-website/pull/2462#discussion_r362104517">app/mailers/notifier.rb</a>:</p>
<pre style='color:#555'>>        @author = @from_user
 
       attach_user_avatar(comment.user)
 
+      headers["In-Reply-To"] = @ref
+      headers["References"]  = @ref
</pre>
<p>I think we could reduce the amount of duplication here by having a <code>set_references</code> helper function and then just doing <code>set_references("diary", comment.diary_entry)</code> etc in each of the three methods?</p>

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