Re: [dmarc-ietf] Ticket #111 - MX/A/AAAA test needs justification

"Murray S. Kucherawy" <superuser@gmail.com> Tue, 25 May 2021 19:39 UTC

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From: "Murray S. Kucherawy" <superuser@gmail.com>
Date: Tue, 25 May 2021 12:39:12 -0700
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To: Douglas Foster <dougfoster.emailstandards@gmail.com>
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Subject: Re: [dmarc-ietf] Ticket #111 - MX/A/AAAA test needs justification
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On Sun, May 23, 2021 at 12:25 PM Douglas Foster <
dougfoster.emailstandards@gmail.com> wrote:

> [...]
> 145 of 169 (86%) of non-verified domains had MX or A records,
> Of the 24 without MX or A records, 23 were spam and 1 was legitimate
> For 20 of the 24 , SPF on the From address returned NXDomain and were
> obvious spam without checking NS
> All of the remaining 4 domains had NS records
>

I believe this means that for 2.4% of the non-verified domains, or 0.65% of
the total domains, the proposed NS check yielded useful signal beyond the
standard checking of MX/A/AAAA.

One surprise for me:
> NS lookup on email3.reachmd.com returns NXDomain, but NS lookup on
> sg.email3.reachmd.com returns NS data.
> I thought that the existence of a subdomain would be sufficient for a
> domain to return NS data.
>

Right, it isn't.

Summary:
> - MX/A produced 11 false positives
>

Is that 11 false positive messages, or 11 false positive unique domains?
If the former, we're talking about around 0.3%.  If the latter, we're
talking about 1.8%.

So based on the data you collected, what conclusion are you proposing?

-MSK