From: Yves-Eric <yemartin@...>
Date: 2009-02-23T11:29:29+09:00
Subject: DNS MX lookup issue: local machine returned as MX for an non-existant 	domain!

Hi all,


Trying to do some email domain validation, I am facing a weird issue
when looking up an MX entry. Here is a three-liner test code:

require 'resolv'
domain = "i-dont-exist-iutjdfuyoxfugy.com"
Resolv::DNS.open { |dns| dns.getresources(domain,
Resolv::DNS::Resource::IN::MX)}

On my development machine, this returns an empty list, as expected
(the domain does not exist, it cannot have an MX record!).
However, in my production environment, the same code returns:
=> [#<Resolv::DNS::Resource::IN::MX:0xb7cde342
@exchange=#<Resolv::DNS::Name: mydomain.com.>, @preference=10>]

It returns the production machine itself as a valid MX for a domain
that does not exist!

I double-checked on the command line that "nslookup -q=mx i-dont-exist-
iutjdfuyoxfugy.com" indeed returns NXDOMAIN...

Could someone please explain to me why this may be happening, and how
to fix it? Howcome Resolv::DNS is returning an MX record for a domain
that does not exist?! As a temporary workaround, I am simply filtering
out mydomain.com from the MX list, but it really bugs me not knowing
what the root of the problem is.


Thank you,

--
Yves-Eric