Re: [dmarc-ietf] Ticket #11 (and #112) - Proposed language

Alessandro Vesely <> Wed, 16 June 2021 11:34 UTC

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To: Douglas Foster <>, IETF DMARC WG <>
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From: Alessandro Vesely <>
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Date: Wed, 16 Jun 2021 13:33:53 +0200
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Subject: Re: [dmarc-ietf] Ticket #11 (and #112) - Proposed language
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On Tue 15/Jun/2021 01:19:03 +0200 Douglas Foster wrote:
> It took me only one day to find examples of this;,non-existent subdomains used 
> on legitimate messages sent by mailing services.  The FROM suffix correctly 
> reflects the parent organization, but the full email suffix does not appear in 
> DNS.

Me too.  I reviewed my logs for 2021 and got this:

88 NXDOMAIN found out of 160,473 messages:
35 bounces (empty mailfrom),
26 not found host in an existing suffix,
27 totally astray.

Except for bounces, which just reflect a poorly configured server, I wouldn't 
swear to their legitimacy.  For the few samples of which I still have the 
score, it was high.

However, to reject based just on NXDOMAIN is too harsh.

> This situation means that we cannot distinguish between valid and invalid
> email suffixes using DNS alone, we must require domain owner signalling.

I'd agree, but the idea of suggesting to signal such lack of registration over 
the DNS is to diabolically persist on an error.