Re: [dmarc-ietf] A policy weaker than quarantine, yet better than none

John R Levine <johnl@taugh.com> Mon, 18 January 2021 17:54 UTC

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Date: 18 Jan 2021 12:54:15 -0500
Message-ID: <7e5b91cc-8ca8-6f7f-4c3e-83e13a85c61d@taugh.com>
From: "John R Levine" <johnl@taugh.com>
To: "Alessandro Vesely" <vesely@tana.it>, "dmarc-ietf" <dmarc@ietf.org>
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Subject: Re: [dmarc-ietf] A policy weaker than quarantine, yet better than none
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On Mon, 18 Jan 2021, Alessandro Vesely wrote:
> On Sun 17/Jan/2021 22:35:36 +0100 John Levine wrote:
>> If I wanted, I could send a dozen replies to this list faking the addresses
>> of previous senders saying that your suggestion is brilliant, or not.
>
> And we tolerate this security hole because...?

Because it is not a problem worth solving in practice.  Mailing lists have 
all sorts of ways to validate submissions beyond looking at the From 
header, ranging from sender challenges to S/MIME signatures.  No list I 
know of turns them on.

> At least, we could specify in the General Record Format that unrecognized 
> policies should be treated as p=none.

Absolutely not.  Any DMARC record with an invalid p= is just broken.  We 
write standards that say how to interoperate, not how to guess what other 
people had in mind when they implemented it wrong.

Regards,
John Levine, johnl@taugh.com, Taughannock Networks, Trumansburg NY
Please consider the environment before reading this e-mail. https://jl.ly