From: Peter Rabbitson (rabbitrabbit.us)
Date: Wed Aug 01 2007 - 11:35:32 CDT

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Jorey Bump wrote:
> Peter Rabbitson wrote:
>
>> This is yet another not strictly postfix related post, please bear
>> with me.
>> My question is simple - is it legal/will it cause any problems if a
>> domain lists two MX records which eventually resolve to the same IP.
>>
>> Here is the rationale: I need to migrate an MX used as backup for many
>> domains to a different IP. The IP will be released into a pool, and
>> possibly reused promptly. If it is assigned to another SMTP server
>> mail might be returned due to the 5xx responses such a server might
>> produce. One way to deal with that would be to change the MX
>> information for all domains, but it will take quite some effort.
>> Another would be to simply change the A record of the MX in question
>> until everything is settled (all domains list the same MX fqdn).
>
>
> And to answer your question, no, it shouldn't be a problem if multiple
> MX records resolve to the same IP address, as long as it's the right one.

Excellent. Since the change will happen next week, and all my A records
have a 6 hour ttl, I will simply point both MXes to the IP of the main
server. So by the time changes actually take place no one will try to
contact the backup MX (except for horribly broken DNS caches which are
not really my problem).

Thank you for the help!

Peter

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