I have two machines running postfix, one is the primary mail server, the other is a backup relay.
Both servers have an MX record, the backup having a lower priority.
Most mail is relayed fine, but the backup occasionally tries to relay mail to it's own FQDN resulting in "mail for domain.com loops back to myself" in the logs and delayed emails.
How can I prevent the backup postfix from attempting to relay to it's own MX record?