Linux Email
by Ian Haycox, Ralf Hildebrandt, David Rusenko, Alistair McDonald, Patrick Ben Koetter, Carl Taylor, Magnus Back
Backup mail servers
Having a backup mail server that can receive messages if the primary 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. However, the advantage of this is very small, as all SMTP servers are required to queue undeliverable messages for at least five days before they are returned to the sender. Granted, by having a backup server it is possible to store unavailable messages for longer time ...
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