postfix reload # Gracefully reload configs postfix log # Monitor in real-time: tail -f /var/log/maillog
In rare cases, the Postfix binaries themselves, or the libraries they depend on, may be corrupted, leading to failure when attempting to launch specific transport services.
The Postfix error "delivery temporarily suspended: unknown mail transport error"
If you use a third-party relay (like SendGrid or Mandrill), incorrect credentials or hostname settings in can trigger this generic error. Broken Milters or Filters:
This ensures upd re-resolves maps more frequently.
Postfix uses a transport map to decide how to deliver mail (e.g., via SMTP, local, or a script). If this map points to a non-existent or misnamed transport, you’ll see this error. This often happens after an upgrade (the "upd" in your subject line).
journalctl -u postfix | grep "unknown mail transport error"