Re: [exim] Avoid mail loops with backup servers

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Author: Matthias Waffenschmidt
Date:  
To: Patrik Jansson
CC: exim users
Subject: Re: [exim] Avoid mail loops with backup servers
Hello,

On Wed, Jan 31, 2007 at 09:25:52AM +0100, Patrik Jansson wrote:
> We have a set of primary mail servers, let's call it A. We also have two
> backup mail servers B and C (which should operate on the same MX
> priority but a slightly different problem occurs even if they wouldn't).
>
> Figure the case where a mail is to be delivered to a particular mail
> server in the set A but that server is down so it is delivered to B
> instead. B then tries to deliver to the primary server but it's still
> down so it goes on in the MX priority and sends the mail to C insteads.
> And here's where the loop begins I think, because C will then re-send it
> to B won't it?


No, it won't, if the priorities are equal.

This behaviour is documented in chapter 17 of the fine manual:

<quote>
MX records that point to the local host, or to any host name that
matches hosts_treat_as_local, are discarded, together with any other
MX records of equal or lower priority.
</quote>

And please, don't steal threads.

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