Temporarily Suspended Unknown Mail Transport Error Postfix Upd Work — Delivery

"delivery temporarily suspended: unknown mail transport error"

• Debian/Ubuntu: /var/log/mail.log
• RHEL/CentOS: /var/log/maillog

Useful commands

• Test the filter manually as the Postfix user:

  sudo -u postfix /path/to/filter --test < some_email.eml
  

• Check for missing libraries:

  ldd /path/to/filter | grep "not found"
  

• Reinstall the filter from your package manager, ensuring all dependencies are met:

  sudo apt-get install --reinstall amavisd-new spamassassin
  

If you use a milter (for signing/scanning) or an external transport (like Dovecot LMTP), ensure those services are running: sudo systemctl status dovecot sudo systemctl status amavis Use code with caution. Copied to clipboard 4. Restart and Flush the Queue Debian/Ubuntu: /var/log/mail

often sit between Postfix and the final destination. If these services crash or if the connection port (often 10024 or 10026) is blocked, the transport becomes unavailable. Chroot & Permission Issues Useful commands

sudo postconf -M dovecot/unix
sudo postconf -M dovecot/unix | awk '$8="/usr/libexec/dovecot/dovecot-lda"; print $0' | sudo postconf -M -

6. Recommendations

• Monitoring: Implement monitoring for the Postfix queue length. Alerts should trigger if the queue size exceeds a defined threshold.
• DNS Redundancy: Ensure multiple valid nameservers are configured to prevent single points of failure in DNS resolution.
• Chroot Maintenance: If using chroot, ensure a cron job or systemd unit copies necessary system files (resolv.conf, hosts, services) into the chroot directory whenever they change on the host system.

Cause: The update relabeled binaries or changed file contexts. Postfix may no longer have permission to execute a transport binary. Debian/Ubuntu: /var/log/mail