If you are running on a system like CentOS or in a Docker container, check if the smtp service is chrooted in master.cf (look for a y in the 5th column). If the chroot environment is incomplete, change this to n and restart Postfix. Also, ensure /etc/services is readable by the postfix user.
for "fatal" or "panic" messages occurring just before the suspension. Validate Configuration : Run the following command to check for syntax errors: postfix check Use code with caution. Copied to clipboard Verify Services If you are running on a system like
after making changes to main.cf or master.cf . for "fatal" or "panic" messages occurring just before
If your partition is 100% full, Postfix will suspend delivery. Check with df -h . If your partition is 100% full, Postfix will
postfix stop postsuper -s # Recreate lost queue structure fsck -y /dev/sdX # Where /var/spool is mounted postfix start
Or use qshape deferred to see the age of stuck emails. If all emails are failing, it's a system-wide transport issue.
Postfix, the rock-solid Mail Transfer Agent (MTA) that underpins a vast swath of the internet’s email infrastructure, is usually a paragon of clarity. It either accepts a message, rejects it with a clear code (like the famous "550 User unknown"), or bounces it back. But the "unknown mail transport error" stands apart. It is the catch-all for the uncatchable—the digital equivalent of "something happened, but we’re not sure what."