Dumb Question is an A or AAAA record required?

Matus UHLAR - fantomas uhlar at fantomas.sk
Thu Jul 9 14:24:38 UTC 2020

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 at fantomas.sk ; http://www.fantomas.sk/
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