[RndTbl] email-receive blacklist?

Adam Thompson athompso at athompso.net
Thu Apr 29 14:31:11 CDT 2021

The usual solution is to create a CNAME for "mail.tecnopolis.ca" pointing to "tecnopolis.ca" and then an MX for tecnopolis.ca pointing to the CNAME (which itself violates RFCs).
Yes, I have seen MTA software that does not follow the RFC, and requires an MX.  I had hoped that was a one-off, but apparently not.

On April 29, 2021 1:53:29 p.m. CDT, Trevor Cordes <trevor at tecnopolis.ca> wrote:
>On 2021-04-29 Colin Stanners wrote:
>> I'm afraid that if I understand the situation correctly, the MXVerify
>> result is not an non-error, it is a real problem, and the likely
>> cause of your issue.
>See the Gilbert reply.  This doesn't jive with the understanding of
>these 2 old hands.
>> That serverfault link is unrelated, you are not sending emails only,
>> this discussion is about your domain receiving email.
>Ya, but its answer re: RFC5321 is correct:
>2.3.5.  Domain Names
>   Only resolvable, fully-qualified domain names (FQDNs) are permitted
>   when domain names are used in SMTP.  In other words, names that can
>   be resolved to MX RRs or address (i.e., A or AAAA) RRs (as discussed
>   in Section 5) are permitted, as are CNAME RRs whose targets can be
>   resolved, in turn, to MX or address RRs.
>So per RFC is the receiving domain can either resolve to MX, *or*
>direct A RR (as my domain did).
>5.1. Locating the Target Host
>   If an empty list of MXs is returned,
>   the address is treated as if it was associated with an implicit MX
>   RR, with a preference of 0, pointing to that host.
>As far as I can tell, 5321 is still in force and not superseded.
>I had a valid, empty (non-existent) MX record set.  That should be
>If you have a different understanding, feel free to RFC-enlighten us!
>Roundtable mailing list
>Roundtable at muug.ca
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