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Date: Tue, 23 Sep 2014 04:11:23 -0400
Message-ID: <CAA8DMBteQszEYQuwjG2XQRoGvbQbMcas45a+Cd11_TLqEAg=8w@mail.gmail.com>
To: Pierre Joye <pierre.php@gmail.com>
Cc: Michael Wallner <mike@php.net>, Kris Craig <kris.craig@gmail.com>, 
	PHP Internals <internals@lists.php.net>
Content-Type: text/plain; charset=UTF-8
Subject: Re: [PHP-DEV] [RFC] Change checkdnsrr() $type argument behavior
From: figureonecpr@gmail.com (Sanford Whiteman)

> if somehost.example.com has the MX, it should return true with
> checkdnsrr('somehost.example.com'). If example has the MX set to
> somehost.example.com or similar, it should return true as well. Or am
> I missing your point?

You are missing it, as there are no MX records involved.  I'm
demonstrating that the function gives incorrect results in the absence
of an MX record because there is a bug in CNAME handling (or a bug in
A handling, if you prefer).

somehost.example.com has no MX RR.  It has a CNAME (per DNS rules, the
CNAME must thus be the only record for somehost.example.com). The
CNAME  points to example.com.

example.com has no MX RR.  It has an A pointing to 1.2.3.4.

checkdnsrr('somehost.example.com') should return false. It returns true.
checkdnsrr('example.com') should return false.  It returns false.

You could try to revise the docs and say, "Oh, it doesn't really mean
an MX lookup, it means an explicit MX *or* implicit MX, like how a
basic smtp-sender works. So that's why the CNAME --> A one returns
true."  Except then 'example.com' should return true as well.  It does
not: it returns false.  Changing the docs does not fix the bug.

BTW, I've been reading SMTP RFCs since we were on good ol' 821, and
I'm plenty intellectually curious. I don't care if a function is
supposed to partially emulate an smtp-sender when verifying a domain,
or if it's supposed to run a dumb DNS MX query.  It either does what
it's supposed to to do or it's broken.

-- S.