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

Fri Feb 26 19:11:59 UTC 2021

On Fri, 2021-02-26 at 12:03 -0700, Grant Taylor via NANOG wrote:
> On 2/26/21 11:46 AM, borg at uu3.net wrote:
> > Well, I bet my legacy system will bounce it for example...
> 
> What specifically is the bounce?
> I thought the purpose of the Null MX was to do two things:
> 1)  Provide as an MX that can't be connected to.2)  Serve as a signal to
> things that know how to interpret it that no mail is to be expected.
> I would expect that some server, if not the MSA, /would/ generate a bounce
> /because/ the email to the domain is undeliverables.

Exactly. Postfix bounces it immediately with an accurate message:

Domain ???.com does not accept mail (nullMX)

This seems preferable to waiting hours or days for a bounce due to not being
able to connect to the A record on port 25 or w/e.
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