Backup Mail Servers

Having a backup server that can receive your messages if your own server is unavailable sounds like a really good idea, but today's reliable Internet connections together with spam, worms, and other rubbish have for the most part made backup mail servers unnecessary and often even harmful. The rationale for having a backup server is that it can receive messages while your primary server is down, and then deliver them to the primary server when it is up again. The advantage of this is, however, very small since all SMTP servers are required to queue undeliverable messages anyway for at least five days before they are returned to the sender. Granted, by having a backup server you can choose to store unavailable messages for longer time than five days, but if your main SMTP server is unavailable longer than five days at a stretch you probably have bigger problems than a few lost messages.

But how does the spam fit in? Because a backup mail server typically does not have the same spam-thwarting configuration as the primary server, spammers often specifically target backup servers in order to bypass the stricter rules of the primary server.