Delivery Temporarily Suspended Unknown Mail Transport Error Postfix Upd _best_ Instant

postcat -q <queue_id>

Verify that those dependent system services are operational: postcat -q &lt

Which (Amavis, Dovecot, MailScanner) do you use to process mail? postcat -q &lt

If your mail server runs out of storage space or runs out of available file system inodes, Postfix cannot write temporary files during the transport phase. postcat -q &lt

: 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

If you use custom routing, check your transport configuration file (usually /etc/postfix/transport ). Open the file to verify the syntax: