If the error appeared after an update (the “upd” clue):
postmap /etc/postfix/transport systemctl restart postfix If the error appeared after an update (the
If the transport requires a DNS lookup that fails, or if an ISP blocks Port 25 , Postfix may defer the transport. Troubleshooting & Fixes If the error appeared after an update (the
typically means Postfix is trying to use a delivery mechanism (transport) that is either misconfigured in or missing entirely from If the error appeared after an update (the
: If Postfix is running in a "chroot" environment, it may lose access to necessary system files (like /etc/services