Delivery Temporarily Suspended Unknown Mail Transport Error Postfix Upd May 2026

: If you are using a third-party milter or content filter (like Postgrey or Amavis ), and that service is crashed or not listening on the expected socket/port, Postfix will suspend delivery to that path. Troubleshooting Steps

: In master.cf , the 5th column indicates whether a service should run in a "chroot" jail. If this is enabled ( y ) but the necessary environment (like /etc/services or library files) isn't correctly mirrored inside the chroot directory, services like the smtp client may fail to resolve protocols or hosts. : If you are using a third-party milter

This status is a "soft failure" or deferral, meaning Postfix will keep the mail in the queue and try again later, but it signal that a underlying configuration or service issue is blocking the path. Primary Causes of the "Unknown Mail Transport Error" This status is a "soft failure" or deferral,