Delivery Temporarily Suspended Unknown Mail Transport Error Postfix Upd _verified_ Guide

Because the failure happened at the "transport" layer rather than the SMTP protocol layer, Postfix does not know exactly why it failed, so it marks the status as "unknown" and places the email in a deferred queue to try again later.

postmap -q "test@example.com" mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf Because the failure happened at the "transport" layer

Note the relay=... field. That tells you which transport failed. Because the failure happened at the "transport" layer

tail -n 100 /var/log/mail.log # OR on some systems: journalctl -u postfix -n 100 Use code with caution. Copied to clipboard Because the failure happened at the "transport" layer