I have a client with a SCO Unix server that uses Microlite BackupEDGE, configured to notify several people, including me, of backup results. The Unix server uses MMDF, but the main mail server is SME Server.
When the SCO server was installed many years ago, it was configured with a domain name that matched the client's business name: let's call it abc.com. This was long before they had any internet presence, and by the time these folks did go out to grab a domain name, abc.com was already taken, so they had to use abcdef.com. We never bothered to update the SCO server, because it wasn't sending mail at that time. When they decided to email backup results rather than printing them, I just configured MMDF quickly (mkdev mmdf), and honestly paid no attention to the fact that it was representing itself as abc.com. The mail went to the group address on the SME server (no sense in maintaining the group in two places) which then passed it along to the members. MMDF was configured not to use DNS, so mail to firstname.lastname@example.org was resolved by /etc/hosts, and sent right out on the local network. The SCO server wasn't supposed to send any other internet mail, so this left it still unable to - no smart host was configured.
This all worked fine for several years. I'd get a regular email with the backup status every morning. But very suddenly, this stopped working and soon after that the SME admin user started getting mail complaining that messages addressed to me at pcunix.com couldn't be delivered.
It didn't take long to figure out what the problem was. My mail server was rejecting mail from email@example.com because abc.com no longer existed. Apparently the owner of that domain had gone out of business or otherwise neglected to renew the name. Understand that abc.com never belonged to my client, and my mail server didn't care that mail supposedly from abc.com actually came from abcdef.com. If it did care, forwarding mail would be impossible. But when abc.com no longer existed at all, it rightfully rejected the mail.
The solution was to reconfigure MMDF on the SCO machine to send mail as firstname.lastname@example.org. It wasn't necessary to change anything else except the hosts file to tell it where abcdef.com actually is.
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More Articles by Tony Lawrence © 2012-07-13 Tony Lawrence
The less accurate your mental model of a given process is, the less accurate is any guess you make about its malfunction. (Tony Lawrence)