multiple mail servers for one domain

Corey Edwards tensai at zmonkey.org
Thu May 14 16:11:49 MDT 2009


On Thu, 2009-05-14 at 15:25 -0600, Daniel C. wrote:
> On Thu, May 14, 2009 at 2:01 PM, William Atteood <wattwood at gmail.com> wrote:
> > Yes.  Setup a second mx say mail2.domain.com
> 
> Won't this result in mail2.domain.com randomly getting emails for
> accounts that should go to mail1.domain.com?  It's my understanding
> that, while mail is *supposed* to be delivered to the MX records in
> order, it doesn't always happen that way, and that it's acceptable to
> deliver mail to any MX record for the domain.

This is slightly deviated from the OP's question, but hopefully useful
to mail admins out there.

You're correct in the way it's *supposed* to work. Well behaved mail
servers will try the MXes in order, and generally that works OK. But
just because your priority 10 mail server is up and running doesn't mean
that everybody has connectivity to it. Some routing issue upstream from
you might prevent certain segments of the Internet from communicating
with it, so they will rightly try your priority 20 server.

The other issue with multiple MXes is that spammers will try your higher
priority servers because they (correctly, oftentimes) assume that spam
filtering will be more lax on those systems. That's especially true if
it's an off-site backup mail server without any knowledge of your spam
rules.

Corey

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