diff --git a/src/applications/metamta/storage/mail/PhabricatorMetaMTAMail.php b/src/applications/metamta/storage/mail/PhabricatorMetaMTAMail.php
index c85e76ca88..d1e5cfa9b8 100644
--- a/src/applications/metamta/storage/mail/PhabricatorMetaMTAMail.php
+++ b/src/applications/metamta/storage/mail/PhabricatorMetaMTAMail.php
@@ -440,9 +440,9 @@ class PhabricatorMetaMTAMail extends PhabricatorMetaMTADAO {
         }
       }
 
+      $mailer->addHeader('X-Phabricator-Sent-This-Message', 'Yes');
       $mailer->addHeader('X-Mail-Transport-Agent', 'MetaMTA');
 
-
       // If the message has mailtags, filter out any recipients who don't want
       // to receive this type of mail.
       $mailtags = $this->getParam('mailtags');