Delivery Temporarily Suspended Unknown Mail Transport Error Postfix Upd Jun 2026

Troubleshooting Postfix: "Delivery Temporarily Suspended: Unknown Mail Transport Error"

relayhost = [smtp.sendgrid.net]:587

transport_maps = hash:/etc/postfix/transport The most frequent culprit is a typo or

Cross-reference the name after the colon (e.g., custom_filter ) with your /etc/postfix/master.cf file. Every transport name used in your mapping must have a corresponding service definition in master.cf .

dovecot unix - n n - - pipe flags=DRhu user=vmail:vmail argv=/usr/lib/dovecot/dovecot-lda -f $sender -d $recipient Use code with caution. (Note: On newer systems using systemd

The most frequent culprit is a typo or a missing service definition in your Postfix configuration files ( /etc/postfix/main.cf or /etc/postfix/master.cf ). If Postfix tries to route mail through a transport service that isn't defined or has incorrect arguments, it throws this error.

Postfix often runs in a chroot jail for security, which can complicate troubleshooting. which can complicate troubleshooting.

<QUEUE_ID> <SIZE> <DATE> <SENDER> (delivery temporarily suspended: unknown mail transport error) <RECIPIENT>

(Note: On newer systems using systemd, use journalctl -u postfix --since "2 hours ago" | grep -C 5 "delivery temporarily suspended" )