Delivery Temporarily Suspended Unknown Mail Transport Error Postfix Upd 〈4K - 360p〉

rm -f /var/spool/postfix/deferred/* /var/spool/postfix/active/*

The error is a symptom, not the disease. Many different underlying issues can lead to Postfix being unable to determine the delivery method for a message. Based on community reports and official documentation, here are the most frequent causes:

Ensure the server can resolve DNS and reach the internet: This could be a local mailbox (e

The "unknown mail transport error" in Postfix, often resulting in temporary suspension, occurs when the server references a delivery method not properly defined in master.cf or if integrated services like Amavis are down. Common troubleshooting involves verifying logs for specific service failures, running postfix check , and ensuring proper permissions for the postfix user.

If the logs show connection refusals for a specific transport (e.g., private/dovecot-lmtp , private/amavis ), restart those dependent services in the correct order: using local transport)

Run a comprehensive configuration check. The postfix check command is invaluable for catching syntax errors and inconsistencies:

In Postfix terminology, a transport is the method by which a message is delivered to its final destination. This could be a local mailbox (e.g., using local transport), an LMTP socket, a Dovecot deliver agent, or a relay host (e.g., smtp transport). an LMTP socket

postqueue -f

If the logs point to a network or DNS issue, confirm connectivity to the destination domain.

: Postfix sub-daemons running inside an isolated jail ( chroot ) that cannot resolve core system network services. Step-by-Step Diagnostic & Resolution Workflow 1. Locate the Root Error in the Mail Log