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

Fri Feb 26 19:18:49 UTC 2021

On 2/26/21 2:10 PM, borg at uu3.net wrote:
> Hmm right... Somehow I tought that having that special Null MX
> will silently discard message... I dont know why...
>
> So, RFC 7505 is pretty much even pointless in my opinion.
> You have to do more.. to pretty much achieve the same..
> Its just easier to not having MX on subdomains that does not serve
> as email destinations.. Less records in DNS..

It should mean that there is no attempt to deliver email, even if the
domain has an A or AAAA record.

>
>
> ---------- Original message ----------
>
> From: Grant Taylor via NANOG <nanog at nanog.org>
> To: nanog at nanog.org
> Subject: Re: Newbie Question: Is anyone actually using the Null MX (RFC 7505)?
> Date: Fri, 26 Feb 2021 12:03:37 -0700
>
> 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.
>
>> I cant speak about Sendmail, qmail, Exim.. when they started supporting it.
> My Sendmail boxes have been dealing with the Null MX just fine.  The
> aforementioned bounce is /expected/ to tell the sender that the destination
> address is bad.
>
>> So, In my opinion changing already working standards in a way
>> that they arent full compat with old systems is imo bad aproach.
> IMHO there is little, if any, effective difference between the Null MX and an MX
> pointing to an unresolvable name or an non-routed IP.  They cause a hard / fast
> failure in an early upstream MTA thus induce a bounce.
>
> Depending on the MSA, the delivery problem may even be presented to the user as
> they are submitting the message to the MSA.
>
>
>
> --
> Grant. . . .
> unix || die
>