Index: app/models/mailer.rb
===================================================================
--- app/models/mailer.rb	(revision 4467)
+++ app/models/mailer.rb	(working copy)
@@ -350,6 +350,7 @@
     headers 'X-Mailer' => 'Redmine',
             'X-Redmine-Host' => Setting.host_name,
             'X-Redmine-Site' => Setting.app_title,
+    		'X-Redmine-Notification-Sender' => User.current.login,
             'Precedence' => 'bulk',
             'Auto-Submitted' => 'auto-generated'
   end