mx selection order

David Sparro dsparro at
Wed Feb 23 18:42:06 UTC 2011

On 2/23/2011 4:56 AM, Stephane Bortzmeyer wrote:
> On Tue, Feb 22, 2011 at 04:37:03PM -0500,
>   David Sparro<dsparro at>  wrote
>   a message of 24 lines which said:
>> it is up to the application how it will use the data.
> MX records are only used by MTA and, no, it is NOT up to the MTA to
> decide how to handle MX records, there is a standard for that, RFC
> 5321, section 5.1.
Yes, but according to the RFC there is room for the MTA to make some 
administrative decisions on which MX records to use:

"However, there MAY also be a configurable
    limit on the number of alternate addresses that can be tried"


"If there are multiple
    destinations with the same preference and there is no clear reason to
    favor one ..."

I'll bet that different MTAs have different definitions of 'clear reason.'


"   Although the capability to try multiple alternative addresses is
    required, specific installations may want to limit or disable the use
    of alternative addresses."


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