Add "X-Auto-Response-Suppress" header to all outgoing mail

Summary: This appears to sometimes be effective (for MS clients), and we've seen it in the wild on inbound mail.

Test Plan: Sent myself some mail, verified it had the right header.

Reviewers: btrahan, vrana, jungejason

Reviewed By: vrana

CC: aran

Maniphest Tasks: T571

Differential Revision: https://secure.phabricator.com/D2241

src/applications/metamta/storage/mail/PhabricatorMetaMTAMail.php

@@ -501,6 +501,9 @@ final class PhabricatorMetaMTAMail extends PhabricatorMetaMTADAO {
       $mailer->addHeader('X-Phabricator-Sent-This-Message', 'Yes');
       $mailer->addHeader('X-Mail-Transport-Agent', 'MetaMTA');
 
+      // Some clients respect this to suppress OOF and other auto-responses.
+      $mailer->addHeader('X-Auto-Response-Suppress', 'All');
+
       // If the message has mailtags, filter out any recipients who don't want
       // to receive this type of mail.
       $mailtags = $this->getParam('mailtags');