Re: [Exim] pri/sec MX on same machine to catch spam

> > Am I correct in assuming that most mailservers (exim, sendmail, qmail,
> > smail, postfix, ...) will try the backup MX if the primary is down or
> > returns a temporary failure code? If so and having 2 MXs on seperate
> > machines, I'm not sure how to ensure that the 2nd has the information before
> > the mailserver gives up on #1 and tries #2.
> >
>
> If primary is down (doesn't answer TCP open), yes, secondary will be
> tried. If primary returns 4xx response code, no, secondary should not
> be tried. Not to say that some systems out there don't do it, but as
> far as I'm aware if the MTA was able to open a TCP connection to the
> lowest-priority MX and get at least an opening banner (without a
> permanent error response code), it shouldn't try higher-priority MXs.

Does it state this in the RFC? (If you know which RFC says it off the top
of your head, I'll go look at it) Is the secondary only useful if the primary
is down (not experiencing temporary errors like misconfiguration).

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