Newbie Question: Is anyone actually using the Null MX (RFC 7505)?

Fri Feb 26 10:19:41 UTC 2021

Dear all,

I put the “Null MX” Record (RFC 7505) into one of my domains yesterday,
then those online mail diagnostic tools out there start getting me worried:

It looks like most of those tools do not recognize the Null MX as a special
case; they just complain that they cannot find the mail server at “.”
[Sarcasm: as if the root servers are going to provide mail service to a
mere mortal like me!]

Among a few shining exceptions (in a good way) is the good ol’
https://bgp.he.net/ which does not show that domain as having any MX record.
[maybe it is also wrong, in the other direction?]

I fear that the MTAs are going to behave that same way, treating my Null MX
as a “misconfigured mail server name” and that my record will mean
unnecessary extra queries to the root servers. [well, minus cache hit]

So, here comes the questions:
1. Is there anyone actively using this Null MX? If so, may I please see
that actual record line (in BIND zone file format) just to satisfy myself
that I wrote mine correctly?
2. Which one makes more sense from the practical point-of-view: having a
Null MX Record for the no-mail domain, or having no MX record at all?

Thanks in advance for all advices,

--

Pirawat.
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