Delivery Temporarily Suspended Unknown Mail Transport Error Postfix Upd Page

Check the SELinux denial:

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). Check the SELinux denial: Postfix uses a transport

postconf -n | grep transport_maps

# On Debian/Ubuntu apt-cache show postfix | grep Version # Find previous version apt install postfix=3.5.6-1 # Example old version # Hold the version to prevent auto-upgrade apt-mark hold postfix postconf -n | grep transport_maps # On Debian/Ubuntu

This usually means Postfix attempted handoff to a transport (local delivery agent, external SMTP, or a pipeline like fetchmail/procmail/virtual) and that transport returned a non-specific/unknown error. Steps to find and fix it: Check the SELinux denial: Postfix uses a transport

: A transport name specified in main.cf (e.g., transport_maps , relayhost , or virtual_transport ) is missing its definition in master.cf .