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

Barry Leiba <> Tue, 03 August 2021 12:22 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id E6DE03A2160 for <>; Tue, 3 Aug 2021 05:22:05 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -1.648
X-Spam-Status: No, score=-1.648 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, FREEMAIL_FORGED_FROMDOMAIN=0.249, FREEMAIL_FROM=0.001, HEADER_FROM_DIFFERENT_DOMAINS=0.001, HTML_MESSAGE=0.001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=no autolearn_force=no
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id cw4mGgzzwOu9 for <>; Tue, 3 Aug 2021 05:22:01 -0700 (PDT)
Received: from ( []) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by (Postfix) with ESMTPS id 10E953A215E for <>; Tue, 3 Aug 2021 05:22:00 -0700 (PDT)
Received: by with SMTP id h9so27927923ljq.8 for <>; Tue, 03 Aug 2021 05:22:00 -0700 (PDT)
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=l4KLQ2208B2IzxoTwqTk57uWen0Cl6dJ6GXFaJuJDqk=; b=Fd3fdB6XvpIS2NgMDK4h/irXCHIFDBPEDWlQWcxdp4PV/2CKQNDZkvzLX1Zmm6ogP9 hB+neAT7iMYgH+bsHle1lupzZSUuX5/aw1mauDkVmt77gOgetBioqt5L9Eu7dZht97xg e6Alsw7+8DGPJg8ziSpMwwLKDeSO94W8wOhYeELxWEUBIs0M4a8/20ZtC7BNr5x7eX84 0W5innaKVsJeFTz/5IbPEiWtAoNEdgKt3RQTkT/biTVOd0Q3/ipZx99P34/ERXi6EUPM qWmKDLLafUEvajAPagmRdWCJILbDyiWIb9I+NjKABSxGrT8D7NujfROeH1A08crEpsVr ZKhg==
X-Gm-Message-State: AOAM532aTkpPllYa5Qm7gZtGOPtCz6ju2ENlan4J6GDybW7xwlvEOy5v f9SsJQMY2UxTHk3eerT4lDzpWsOSiKjkC66eKAwtAEGe
X-Google-Smtp-Source: ABdhPJzZV4g8dsFkv8A1nIFhp1oLuai/yHJBkBjLDlh7zWOe9uVO+AL3d+A1ZB+X5EPa0WrFIs5R1oMZkTxsYQPEBI8=
X-Received: by 2002:a2e:9788:: with SMTP id y8mr14828234lji.75.1627993318903; Tue, 03 Aug 2021 05:21:58 -0700 (PDT)
MIME-Version: 1.0
References: <> <20210803021005.EE5CF257D352@ary.qy> <>
In-Reply-To: <>
From: Barry Leiba <>
Date: Tue, 3 Aug 2021 08:21:47 -0400
Message-ID: <>
To: Todd Herr <>
Content-Type: multipart/alternative; boundary="0000000000007853a305c8a6bb80"
Archived-At: <>
Subject: Re: [dmarc-ietf] Some Proposed Language for a New pct Tag Defintion
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: "Domain-based Message Authentication, Reporting, and Compliance \(DMARC\)" <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Tue, 03 Aug 2021 12:22:06 -0000

The problem I have with leaving pct=0 in as the only (non-default) value is
that it locks history into the protocol.  It makes no sense to have a
binary situation specified by a tag called “pct” that is either 0 or 100.

If we’re leaving this in as a binary thing, (1) we’re already incompatible
with deployments that do pct=20 or whatever, so (2) we might better make it
a y/n or t/f valued tag for that function, deprecate pct entirely, and
leave text in a backward-compatibility section explaining what happened.

I just think that the pct= 0 or 100 thing won’t wear well and will appear
tattered quickly.


On Tue, Aug 3, 2021 at 8:08 AM Todd Herr <todd.herr=> wrote:

> On Mon, Aug 2, 2021 at 10:10 PM John Levine <> wrote:
>> It appears that Todd Herr  <> said:
>> >> I like simple, but I also like the idea of a separate section that
>> >discusses the history of the pct tag and why the old values won't work
>> any
>> >longer.
>> OK except:
>> >   remains the default, and "0".  The value of "0" took on unintended
>> >   significance during the experimental stage as a value used by some
>> >   intermediaries and mailbox providers as an indicator to either
>> >   deviate from standard handling of the message and/or to alter the
>> >   substance of reports generated, ...
>> Alter the reports?  Huh?  I was under the impression that the policy
>> didn't
>> affect the reports, much less the pct.
> My apologies...
> My memory of the effect of the policy "p=quarantine; pct=0" vis-a-vis how
> Google handles a domain's mail was faulty. I remember when working to
> implement DMARC at $JOB[-1] for our corporate domain, I was seeing data in
> the agg reports from Google when we were at p=none that led me to ask "WTF
> are those hosts?" and digging around the various corners of the internet
> unearthed the unknown at the time to me fix of "Yeah, you gotta be at
> p=quarantine; pct=0" to get reports from Google that make sense.
> There are several years old threads on mailop that speak to this topic,
> with outsiders asserting that what is in fact happening is Google Groups is
> rewriting the From when it's p=quarantine; pct=0, and Brandon Long from
> Google in the thread doesn't challenge that assertion, so I'll remove
> reference to the reporting alteration.
> --
> *Todd Herr* | Technical Director, Standards and Ecosystem
> *e:*
> *m:* 703.220.4153
> This email and all data transmitted with it contains confidential and/or
> proprietary information intended solely for the use of individual(s)
> authorized to receive it. If you are not an intended and authorized
> recipient you are hereby notified of any use, disclosure, copying or
> distribution of the information included in this transmission is prohibited
> and may be unlawful. Please immediately notify the sender by replying to
> this email and then delete it from your system.
> _______________________________________________
> dmarc mailing list