Path: csiph.com!newsfeed.xs4all.nl!newsfeed9.news.xs4all.nl!feeder.usenetexpress.com!tr2.eu1.usenetexpress.com!news.uzoreto.com!news.etla.org!nntp-feed.chiark.greenend.org.uk!ewrotcd!usenet-its.stanford.edu!usenet.stanford.edu!not-for-mail
From: Matus UHLAR - fantomas <uhlar@fantomas.sk>
Newsgroups: comp.protocols.dns.bind
Subject: Re: Dumb Question is an A or AAAA record required?
Date: Thu, 9 Jul 2020 16:24:38 +0200
Lines: 27
Approved: bind-users@lists.isc.org
Message-ID: <mailman.677.1594304652.942.bind-users@lists.isc.org>
References: <B1C7B197-34CE-42AB-92CC-69F65B35D3FD@kreme.com> <7ab19939-3025-c874-e5a4-97721eb435fc@ripe.net> <ep8egf1jv84i97uev69vr17ld66g4fave6@m78> <20200709142438.GA30977@fantomas.sk>
NNTP-Posting-Host: lists.isc.org
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii; format=flowed
X-Trace: usenet.stanford.edu 1594304686 19514 149.20.1.60 (9 Jul 2020 14:24:46 GMT)
X-Complaints-To: action@cs.stanford.edu
To: bind-users@lists.isc.org
Return-Path: <uhlar@fantomas.sk>
X-Original-To: bind-users@lists.isc.org
Delivered-To: bind-users@lists.isc.org
X-Authentication-Warning: fantomas.fantomas.sk: uhlar set sender to uhlar@fantomas.sk using -f
Mail-Followup-To: bind-users@lists.isc.org
Content-Disposition: inline
In-Reply-To: <ep8egf1jv84i97uev69vr17ld66g4fave6@m78>
User-Agent: Mutt/1.10.1 (2018-07-13)
X-Spam-Status: No, score=-0.0 required=5.0 tests=SPF_HELO_PASS,SPF_PASS autolearn=disabled version=3.4.2
X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on mx.pao1.isc.org
X-BeenThere: bind-users@lists.isc.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: BIND Users Mailing List <bind-users.lists.isc.org>
List-Unsubscribe: <https://lists.isc.org/mailman/options/bind-users>, <mailto:bind-users-request@lists.isc.org?subject=unsubscribe>
List-Archive: <https://lists.isc.org/pipermail/bind-users/>
List-Post: <mailto:bind-users@lists.isc.org>
List-Help: <mailto:bind-users-request@lists.isc.org?subject=help>
List-Subscribe: <https://lists.isc.org/mailman/listinfo/bind-users>, <mailto:bind-users-request@lists.isc.org?subject=subscribe>
X-Mailman-Original-Message-ID: <20200709142438.GA30977@fantomas.sk>
X-Mailman-Original-References: <B1C7B197-34CE-42AB-92CC-69F65B35D3FD@kreme.com> <7ab19939-3025-c874-e5a4-97721eb435fc@ripe.net> <ep8egf1jv84i97uev69vr17ld66g4fave6@m78>
Xref: csiph.com comp.protocols.dns.bind:15954

On 09.07.20 15:06, Matthew Richardson wrote:
>On a related issues there were (perhaps long ago) issues if the A record
>for a domain had an SMTP server on it, where email could sometimes be
>delivered to that A record rather than the MX.  I had (again long ago:
>10-15 years) actually seen this occur.

If there is MX record for a domain, a MTA MUST only use MX record when
delivering to that domain. 

If there is no MX record for a domain, but an A record is available, MTA
uses default MX with preference of 0 pointing to that A records.

This is how it's defined to work, this is not "an issue about that".

>Do people think that this problem could still occur these days?  What sort
>of transient (presumably DNS) failure might cause an SMTP server to deliver
>to A rather than MX?

the only DNS failure that could cause this (and I can think of now) is if
DNS server incorrectly returned NODATA for MX record (effectively saying
there's no MX).

-- 
Matus UHLAR - fantomas, uhlar@fantomas.sk ; http://www.fantomas.sk/
Warning: I wish NOT to receive e-mail advertising to this address.
Varovanie: na tuto adresu chcem NEDOSTAVAT akukolvek reklamnu postu.
Spam = (S)tupid (P)eople's (A)dvertising (M)ethod