Delivery Temporarily Suspended Unknown Mail Transport Error Postfix Upd -

The server is out of RAM, disk space, or available process slots.

If the queue is full of thousands of these errors and you know the destination domain is permanently dead:

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

The Postfix spool directory should be owned by the postfix user. If you suspect permission problems, you can run a filesystem check: The server is out of RAM, disk space,

A particularly important cause, especially relevant to the keyword "upd" in the prompt, is a . Cases have been documented where updating the GNU C Library ( glibc ) from version 2.32 to 2.33 caused the smtp process to fail with fatal: unknown service: smtp/tcp . This was ultimately traced to a change in the Name Service Switch (NSS) logic within glibc . A full system update can also reset or overwrite critical Postfix configuration files, re-introducing old settings or breaking custom ones.

The filter binary was recompiled but its dependencies (e.g., Perl modules, libssl) are now incompatible with the version Postfix is trying to run.

Dovecot changed the location of its binary or the protocol for LMTP sockets. For example, dovecot-lda (Local Delivery Agent) may have moved from /usr/lib/dovecot/deliver to /usr/libexec/dovecot/dovecot-lda . Cases have been documented where updating the GNU

If you use a third-party delivery agent (like for local delivery or Amavis for scanning), Postfix communicates via a Unix socket or a TCP port. If that socket is missing or Postfix doesn't have permission to "talk" to it, the transport error appears. The Fix: Ensure the backend service is actually running. Check Dovecot: systemctl status dovecot

su - filter /usr/bin/spamfilter.sh test@test.com recipient@domain.com

Look for lines containing fatal , panic , or error immediately before the suspension notice. Common culprits include: Permissions issues on a socket (e.g., Dovecot LMTP). The filter binary was recompiled but its dependencies (e

Check the SELinux denial:

postqueue -f