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

Alessandro Vesely <vesely@tana.it> Mon, 18 January 2021 12:09 UTC

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To: John Levine <johnl@taugh.com>, dmarc-ietf <dmarc@ietf.org>
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From: Alessandro Vesely <vesely@tana.it>
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Date: Mon, 18 Jan 2021 13:09:15 +0100
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Subject: [dmarc-ietf] A policy weaker than quarantine, yet better than none
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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...?

On Tue 15/Dec/2020 10:50:10 +0100 I wrote:
> I wish there was an intermediate policy, call it p=mlm-validate, that 
> directs [an intermediate forwarder such as a mailing list] to reject if not
> authenticated, while final recipients can accept it as if p=none.

At least, we could specify in the General Record Format that unrecognized 
policies should be treated as p=none.  Currently, this is subject to the 
existence of a rua= tag.  In Policy Discovery, we have:

    6.  If a retrieved policy record does not contain a valid "p" tag, or
        contains an "sp" tag that is not valid, then:

        1.  if a "rua" tag is present and contains at least one
            syntactically valid reporting URI, the Mail Receiver SHOULD
            act as if a record containing a valid "v" tag and "p=none"
            was retrieved, and continue processing;

        2.  otherwise, the Mail Receiver applies no DMARC processing to
            this message.

(Such optimization should be inferred by the implementation, no?)