[afnog] Two mail servers in the same domain

[Stephane Bortzmeyer]

On Fri, Dec 12, 2008 at 10:37:37PM -0800,
 SM <sm at resistor.net> wrote 
 a message of 27 lines which said:

> You can have a mail server acting as a backup in case the first mail
> server is unreachable.

Which is useless most of the time: unlike synchronous services like
XMPP or HTTP, email is asynchronous. Clients will just automatically
retry.

> Use the relay_domains setting in the Postfix configuration to specific 
> the domain on the second mail server.

There is much more in the configuration of a secondary MX! Since it
will be targeted in priority by spammers, you have to be sure it is
not the weakest link (it is quite common for secondary MX servers to
have less anti-spam protection).

Most of the times, it is not worth the trouble.