Is Hotmail in the habit of ignoring MX records?

Mark Andrews marka at
Fri Jul 27 02:45:37 UTC 2012

In message <B59A4092-CE2F-44E4-84F9-77C18493AD95 at>, Michael J Wise writ
> On Jul 26, 2012, at 6:34 PM, Mark Andrews wrote:
> > In message <A9A5C64B-831D-42BF-8A38-56CC3B9BAF48 at>, Michael J =
> Wise writ
> > es:
> >>=20
> >> On Jul 26, 2012, at 1:35 AM, Lou Katz wrote:
> >>=20
> >>> The domain is
> >>=20
> >> Why does have MX records?
> >=20
> > Why do you care?  There is nothing wrong with having explict MX
> > records and they generally take up less room in a DNS cache then
> > the negative response does especially if it is DNSSEC signed.
> >=20
> >> And they're different.
> >=20
> > Again why do you care?
> Why do *I* care?
> I don't.
> I'm just trying to find the weird bit that maybe is causing hotmail to =
> stumble.
> And maybe an endless loop for an MX lookup might be what is causing =
> hotmail to panic and throw out the MX records.

You don't lookup MX records for MX targets.  This is basic MTA

If the MX lookup fails, as apposed to returns nodata, you don't
lookup the A/AAAA records and synthesis a MX record.  You treat it
as a soft error and queue for retry later.  Again this is basic MTA

You don't depend on ALL (ANY) returning MX records as they may not
be in the cache.  You need to make a explict MX query you get no
MX records are returned in response to a ALL query.

Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at

More information about the NANOG mailing list