The Postfix error "delivery temporarily suspended: unknown mail transport error" is
Postfix uses a filesystem-based queue (/var/spool/postfix). If an inode is corrupted or the disk is full (100% usage), the upd process cannot lock or read queue files. Debian/Ubuntu: /var/log/mail
: Ensure external filters (like Amavis) are running. If they are down, Postfix will cannot "transport" mail to them. Flush the Queue : After fixing the configuration, use postqueue -f to force a retry of all deferred messages. Virtualmin Community a cryptic signal that your mail server has
nano /etc/postfix/master.cf
a cryptic signal that your mail server has encountered a structural mismatch between its instructions and its available tools Debian/Ubuntu: /var/log/mail