Procmail (or the custom binary) was removed or replaced by a stub that returns a non-zero exit code. Many distributions removed Procmail by default after 2020.
If you use Dovecot for local delivery, Postfix often communicates via a socket. If Postfix doesn't have permission to write to that socket, you'll see this error. Check your Dovecot configuration (usually /etc/dovecot/conf.d/10-master.conf ). Ensure the postfix user has access: Procmail (or the custom binary) was removed or
The content filter (like Amavis or SpamAssassin) might be down. 2. Verify Transport Settings Procmail (or the custom binary) was removed or
The update relabeled binaries or changed file contexts. Postfix may no longer have permission to execute a transport binary. Procmail (or the custom binary) was removed or
