Dnia 30.01.2025 o godz. 14:03:51 Matus UHLAR - fantomas via mailop pisze:
Nowadays, we can mark domains that don't send mail using Null MX (rfc 7505).
But this needs explicit record to say "this domain does not send/receive e-mail"
Requiring MX to explicitly state "this domain does send/receive
mail" would clean up field a bit.
On 30.01.25 18:18, Jaroslaw Rafa via mailop wrote:
Consider a classical scenario (may be an university, as this model was very
common in universities): there is a domain example.org, which does not have
an A/AAAA record on its own, and there are many servers within this domain
(often having "funny" names - university people like it: frodo.example.org,
gandalf.example.org, rabbit.example.org, alice.example.org etc.) Each of
these servers runs a MTA - you may think of it as of each university
department having their own mail server (which is also very common in
universities: each department has their own rules for doing things and they
cannot accept to be put under one single "government").
I guess that the exactly opposite scenario: domain has A/AAAA records, but
is not used to send/receive mail, is much more common nowadays.
Do you really think it's reasonable to put MX records for all these machines
into the DNS, that basically duplicate the A/AAAA records? What for? For
me similar scenario (multiple hosts in a network and mail exchanged between
these hosts) was always a strong proof that the fallback to A/AAAA should
and must remain.
... and it makes much more sense to explicitly state "this domain is used as mail
sender/recipient domain" than mark all domains who are not used that way.
That results in much less DNS records and easier checking.
It appears that Matus UHLAR - fantomas via mailop <uh...@fantomas.sk> said:
I'm sure we could reject many mail coming from hosts without MX record and
without running MTA on port 25, thus from undeliverable senders.
On 30.01.25 13:28, John Levine via mailop wrote:
That would reject all mail from Gmail and every other large provider I know.
Seems a bit extreme. It'd even reject mail from my tiny system since the
inbound and outbound MTAs are on different IPs and neither has the name
of the domain I use for mail.
It would not, because gmail.com does have MX records.
Perhaps I should have stated "mail from domains without MX records in RHS".
It would reject mail from @mail-il1-f197.google.com, because that name does
not have MX record. And that host doesn't allow SMTP in, so it's a win here.
Requiring MX to explicitly state "this domain does send/receive mail" would
clean up field a bit.
It would, but fallback to A has been part of SMTP since RFC 974 in 1986 and it's
not going away now.
I believe it should go away asap.
RFC 974 also descrived the WKS (Well Known Services) record
that a domain could publish to say which services it supports, but that never
worked. We invented null MX several decades later as a simpler alternative
which does actually work if you use it.
Null MX is just a work around the current state which expect every domain
being used for mail by default.
IMHO it makes much more sense to incidate "this domain is used for mail"
than mark all domains who are not used that way.
I believe these are much more common.
--
Matus UHLAR - fantomas, uh...@fantomas.sk ; http://www.fantomas.sk/
Warning: I wish NOT to receive e-mail advertising to this address.
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