Hello, It is suggested to provide list of relay_domains explicitly for the backup mx: http://www.postfix.org/STANDARD_CONFIGURATION_README.html#backup
But another solution is to set "permit_mx_backup" for "smtp_relay_restrictions". It seems to be a flexible approach (since only DNS should be changed), but for some reason this method hasn't been mentioned in the document. Does it have drawbacks? By the way, should I explicitly set "permit_mx_backup_networks" to my primary MX if I use "permit_mx_backup"? I can't imagine any case when this feature could be misused (except DNS spoofing probably) Thank you. Ilya.
