Is Hotmail in the habit of ignoring MX records?

Mon Jul 30 20:07:37 UTC 2012

On Mon, Jul 30, 2012 at 7:03 AM, Mark Andrews <marka at isc.org> wrote:
> In message <CAP-guGVuNoqRhGw_UMVQtkJ-zToM8NGB2aLk=wjtc0J7Fh8XUw at mail.gmail.com>, William Herrin writes:
>> What *should* happen here is that the guy's web server should reject
>> the port 25 connection (an SMTP soft fail condition) and on the next
>> retry hotmail should find the MX record and follow it.
>
> No.  It is perfectly legal for A to accept mail for B, B for C, C
> for D and D for A with all mail being delivered to a host with a
> different name than the mail domain.  It is not and never has been
> correct processing to lookup addresses records for a domain if the
> MX lookup fails.  nodata/nxdomain are not failures.

Hi Mark,

If you can reference where in the SMTP RFC it offers an authoritative
explanation what to do when merging results from various naming
systems where one but not all of the naming systems has generated an
error then let's read it. If not... your common sense says one thing,
mine says another and folks implementing mail systems should be aware
the implications.

Until then, my view is that a lookup failure when seeking an MX record
should only block the MTA from seeking an address record in the DNS.
It should still seek an address record in higher priority naming
systems and use it if it finds one. If correct, and I think it is,
that's a pretty subtle thing to program for... something easily gotten
wrong.

Regards,
Bill Herrin

-- 
William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
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