Path: csiph.com!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Salvador Mirzo <smirzo@example.com>
Newsgroups: comp.mail.misc
Subject: Re: mail @example.com without dns a-record for example.com
Date: Mon, 23 Dec 2024 10:23:06 -0300
Organization: A noiseless patient Spider
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Grant Taylor <gtaylor@tnetconsulting.net> writes:

> On 12/22/24 12:07, Kalevi Kolttonen wrote:
>> The email standards do not require a-record ...
>
> Not for the domain name with the MX record.
>
> But there needs to be an A and / or AAAA record for the FQDN that the
> MX record references.

Here's a passage from RFC 5321 that confirms this:

   --8<-------------------------------------------------------->8---
   5.1.  Locating the Target Host

   Once an SMTP client lexically identifies a domain to which mail will
   be delivered for processing (as described in Sections 2.3.5 and 3.6),
   a DNS lookup MUST be performed to resolve the domain name (RFC 1035
   [2]).  The names are expected to be fully-qualified domain names
   (FQDNs) [...]

   [...]

   When a domain name associated with an MX RR is looked up and the
   associated data field obtained, the data field of that response MUST
   contain a domain name.  That domain name, when queried, MUST return
   at least one address record (e.g., A or AAAA RR) that gives the IP
   address of the SMTP server to which the message should be directed.
   --8<-------------------------------------------------------->8---

>> ... so this must one of Gmail's quirks.
>
> I wonder if this might be a Google'ism wherein they saw / cached an A
> record and are now cross that there isn't one.  <something>
> <something> security <something> false test result.

Thanks for bringing that up.  It turns out it just confusion on my part.