Re: [dmarc-ietf] Consensus Sought - Ticket #47 (Removal of "pct" tag) - With Interim Notes

Alessandro Vesely <vesely@tana.it> Thu, 03 June 2021 11:07 UTC

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From: Alessandro Vesely <vesely@tana.it>
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Subject: Re: [dmarc-ietf] Consensus Sought - Ticket #47 (Removal of "pct" tag) - With Interim Notes
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On Thu 03/Jun/2021 05:45:33 +0200 Murray S. Kucherawy wrote:
> I don't understand what "demeaning a domain's policy" means.


I meant to say that p=quarantine; pct=0 is to be considered a strict policy to 
all effects.  Saying so should prevent reasoning something like "Oh, they said 
quarantine, but since pct=0 it is somewhat faked, so I'll skip X", where X 
could be rewriting From:, displaying a BIMI image, record aggregate data, or 
any other action that might depend on the policy.  That is to say pct=0 does 
not alter the value of p=, otherwise testing becomes a nightmare.

Perhaps my point would be obvious if the protocol allowed floating point 
values.  Setting pct=1e-37 would have effects equivalent to pct=0, and setting 
a boundary somewhere to distinguish what is valid from what is not would show 
up all of its arbitrariness.


Best
Ale
-- 

> On Fri, May 28, 2021 at 10:20 AM Alessandro Vesely <vesely@tana.it> wrote:
>> On Fri 28/May/2021 17:43:37 +0200 Todd Herr wrote:
>>>
>>> Consensus on Ticket #47 <https://trac.ietf.org/trac/dmarc/ticket/47>
>>> (Removal of "pct" tag) was reached during the May 27 DMARC Interim to
>>> keep the tag, but to rewrite its definition in whole or in part to make
>>> its usage better understood. >>
>>
>> I think the text in RFC 7489 is quite good.  Perhaps a word could be added
>> for pct=0; for example:
>>
>> OLD
>>     pct:  (plain-text integer between 0 and 100, inclusive; OPTIONAL;
>>        default is 100).  Percentage of messages from the Domain Owner's
>>        mail stream to which the DMARC policy is to be applied.  However,
>>        this MUST NOT be applied to the DMARC-generated reports, all of
>>        which must be sent and received unhindered.  The purpose of the
>>        "pct" tag is to allow Domain Owners to enact a slow rollout
>>        enforcement of the DMARC mechanism.  The prospect of "all or
>>        nothing" is recognized as preventing many organizations from
>>        experimenting with strong authentication-based mechanisms.  See
>>        Section 6.6.4 for details.  Note that random selection based on
>>        this percentage, such as the following pseudocode, is adequate:
>>
>>         if (random mod 100) < pct then
>>           selected = true
>>         else
>>           selected = false
>>
>> NEW
>>     pct:  (plain-text integer between 0 and 100, inclusive; OPTIONAL;
>>        default is 100).  Percentage of messages from the Domain Owner's
>>        mail stream to which the DMARC policy is to be applied.  However,
>>        this MUST NOT be applied to any other use, such as skipping DMARC
>>        reports or demeaning a domain's policy.  The purpose of the
>>        "pct" tag is to allow Domain Owners to enact a slow rollout
>>        enforcement of the DMARC mechanism.  Using this tag, organizations
>>        can experiment with strong authentication-based mechanisms while
>>        lowering or even voiding the risk of non-delivery.  See Section
>> 6.6.4
>>        for details.  Note that random selection based on this percentage,
>>        such as the following pseudocode, is adequate:
>>
>>         if (random mod 100) < pct then
>>           selected = true
>>         else
>>           selected = false
>>
>> jm2c
>> Ale
>> --
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