Problem:


Gmail senders are not receiving bounce notifications when they send emails to non-existent recipient IDs.


Reason:

  1. On SpamTitan, the email is marked as bounced because the recipient ID does not exist.
  2. The MAILER-DAEMON sends a failure notification to Gmail, but Gmail’s server rejects the bounce message due to its updated policies.
  3. Gmail rejects the bounce email with the following error:
    

    550 5.7.26 This mail has been blocked because the sender is unauthenticated.  Gmail requires all senders to authenticate with either SPF or DKIM.  Authentication results: DKIM = did not pass, SPF = did not pass 
  4. When our MAILER-DAEMON@mithi.com sends bounce notifications, the envelope sender (<>) is blank, preventing Gmail from verifying SPF and DMARC, which results in the bounce notification being rejected.