Re: [dmarc-ietf] Some Proposed Language for a New pct Tag Defintion

[Todd Herr <[e-mail]>]

On Tue, Aug 3, 2021 at 3:59 PM Dave Crocker <[e-mail]> wrote:

> On 8/3/2021 12:54 PM, Todd Herr wrote:
> > 2. Define a tag named "t", in a fashion somewhat similar to the t= tag
> > available for DKIM public key records, as follows:
>
> A reasonable suggestion, based on the extended discussion.
>
> I have a devil's advocate question, with two purposes.  One is because I
> really am interested in understanding this better.  The second is
> because it might prompt the additional of some explanatory text, to that
> future readers of the spec will also understand this better:
>
> My question:  what does this accomplish, of significant benefit, that
> p=none does not?
>

To cite one example, "p=quarantine; pct=0" triggers rewriting of the
"From:" header at some intermediaries (such as Google groups) where
"p=none" does not.

I cannot articulate how such rewriting helps a domain owner eventually move
to a policy of p=quarantine or p=reject with no pct tag.

That doesn't mean that I think it's not a useful setting on the journey
from p=none to something stronger; it only means that I can't remember the
particulars of the rewriting that takes place and how the domain owner can
take advantage of information revealed by the rewriting in order to
eventually remove the pct tag.

It might be this:

   - p=none: I as a domain owner receive aggregate reports showing all mail
   that I originated (and obviously stuff I didn't), with some of my
   originated mail flowing through intermediaries
   - p=quarantine; pct=0: I as a domain owner receiving reports showing all
   mail that I originated except for mail that flowed through intermediaries
   that do From: header rewriting. I can then examine the differences in the
   reports, suss out which intermediaries aren't rewriting the From: header,
   and decide if I care enough about the volume I'm sending to those
   intermediaries to have it affect my decision to move to a stronger
   assessment policy.

The above all pre-supposes that p=quarantine or p=reject will also cause
those intermediaries that rewrite when they see pct=0 to rewrite when they
don't. That may be a valid assumption, but I'd rely on someone with more
knowledge of the state of play here to speak to the topic.

-- 

*Todd Herr* | Technical Director, Standards and Ecosystem
*e:* [e-mail]
*m:* 703.220.4153

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