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Re: mail @example.com without dns a-record for example.com

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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.

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mail @example.com without dns a-record for example.com Salvador Mirzo <smirzo@example.com> - 2024-12-22 13:05 -0300
  Re: mail @example.com without dns a-record for example.com Grant Taylor <gtaylor@tnetconsulting.net> - 2024-12-22 10:36 -0600
  Re: mail @example.com without dns a-record for example.com Claus Aßmann <INVALID_NO_CC_REMOVE_IF_YOU_DO_NOT_POST_ml+sendmail(-no-copies-please)@esmtp.org> - 2024-12-22 12:22 -0500
    Re: mail @example.com without dns a-record for example.com Salvador Mirzo <smirzo@example.com> - 2024-12-23 10:18 -0300
  Re: mail @example.com without dns a-record for example.com kalevi@kolttonen.fi (Kalevi Kolttonen) - 2024-12-22 18:07 +0000
    Re: mail @example.com without dns a-record for example.com Grant Taylor <gtaylor@tnetconsulting.net> - 2024-12-22 22:07 -0600
      Re: mail @example.com without dns a-record for example.com Salvador Mirzo <smirzo@example.com> - 2024-12-23 10:23 -0300
  Re: mail @example.com without dns a-record for example.com John Levine <johnl@taugh.com> - 2024-12-22 21:00 +0000
    Re: mail @example.com without dns a-record for example.com Salvador Mirzo <smirzo@example.com> - 2024-12-23 10:08 -0300
      Re: mail @example.com without dns a-record for example.com Salvador Mirzo <smirzo@example.com> - 2024-12-23 22:01 -0300

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