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Re: [dmarc-ietf] Second WGLC for draft-ietf-dmarc-psd: Definition of NP

"Chudow, Eric B CIV NSA DSAW (USA)" <eric.b.chudow.civ@mail.mil> Fri, 20 November 2020 11:29 UTC

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From: "Chudow, Eric B CIV NSA DSAW (USA)" <eric.b.chudow.civ@mail.mil>
To: 'John Levine' <johnl@taugh.com>, "'dmarc@ietf.org'" <dmarc@ietf.org>
Thread-Topic: [dmarc-ietf] Second WGLC for draft-ietf-dmarc-psd: Definition of NP
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Date: Fri, 20 Nov 2020 11:29:29 +0000
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References: <553D43C8D961C14BB27C614AC48FC03128116494@UMECHPA7D.easf.csd.disa.mil> <20201120040420.B3F4727A02FB@ary.qy>
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Subject: Re: [dmarc-ietf] Second WGLC for draft-ietf-dmarc-psd: Definition of NP
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Thank you, John. I agree that it's an edge case and not worth addressing separately. 

Eric Chudow
DoD Cybersecurity Mitigations

-----Original Message-----
From: John Levine <johnl@taugh.com> 
Sent: Thursday, November 19, 2020 11:04 PM
To: dmarc@ietf.org
Cc: Chudow, Eric B CIV NSA DSAW (USA) <eric.b.chudow.civ@mail.mil>
Subject: Re: [dmarc-ietf] Second WGLC for draft-ietf-dmarc-psd: Definition of NP

In article <553D43C8D961C14BB27C614AC48FC03128116494@UMECHPA7D.easf.csd.disa.mil> you write:
>Section 2.7. defines a non-existent domain as "a domain for which there 
>is an NXDOMAIN or NODATA response for A, AAAA, and MX records.  This is 
>a broader definition than that in NXDOMAIN [RFC8020]." This should be sufficient for determining that the domain is not intended to be used and therefore could have a more stringent policy applied.
>
>The idea of looking for a "mail-enabled domain" based on if an "MX record exists or SPF policy exists" is interesting.
>Although there may be domains that send email but not receive email and so may not have an MX record.

These days I think you will find that if the domains in your bounce address and your From: headers don't have an MX or A record, very few recipients will accept your mail. This seems like an edge case. In practice I find that the domains caught by the Org domain or I suppose PSD have A records but no mail server because they're actually web hosts rather than mail hosts.

We have the Null MX to indicate that a domain receives no mail and SPF plain -all to indicate that it sends no mail so I hope we don't try to reinvent these particular wheels.

R's,
John

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