Re: [dmarc-ietf] A policy for direct mail flows only, was ARC questions

Michael Thomas <> Sat, 05 December 2020 18:37 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id CE3CE3A0B18 for <>; Sat, 5 Dec 2020 10:37:41 -0800 (PST)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -1.652
X-Spam-Status: No, score=-1.652 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, HEADER_FROM_DIFFERENT_DOMAINS=0.249, NICE_REPLY_A=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001] autolearn=no autolearn_force=no
Authentication-Results: (amavisd-new); dkim=pass (2048-bit key)
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id nQBVk3bPigia for <>; Sat, 5 Dec 2020 10:37:40 -0800 (PST)
Received: from ( [IPv6:2607:f8b0:4864:20::102d]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by (Postfix) with ESMTPS id A3D1C3A0B1A for <>; Sat, 5 Dec 2020 10:37:40 -0800 (PST)
Received: by with SMTP id lb18so2463571pjb.5 for <>; Sat, 05 Dec 2020 10:37:40 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20150623; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-transfer-encoding:content-language; bh=Ozs9LgG0kL0iWRzemovgDuwKi2eebgUesInkE1JaLmE=; b=kfOIpErYmuE/UFW3UiL4swunQX4p4p3nHgZZcXcGTEgYB/yqXT/fU7zcyZofZSG449 XpIQKiYZevsGxfj1JTR8179A7mOjAnj6rjhegQWwoPHKJ65keSjupKyH6fNoelPD1wSN yWOfCW4jZmp5XDzlLpwwO+w67/cV6UMm5EOkh9O7QzBpsBYLM5X7OfoOakHTsLWkQcY5 GeL/aPP9jaVFZNR3Poy0n3hSQE1xWsRXga3cqQAmkUxtfiu7saRO2NMvJ41ukm2LEsbh mHvKd0gotfDm++0qRWAp6RUJqapSkwVM42OKrs/56OFe0ryhlrlf4pMbuPpIlBKOUdJb AoPg==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :content-language; bh=Ozs9LgG0kL0iWRzemovgDuwKi2eebgUesInkE1JaLmE=; b=Za6k7/g9aBqpsUXe5/VJVC8E/8aQr9v1Sat044VgZ6c4J+lWjFs4uzEl0Q0xmT2Zir LUrvrpjIXkFA6QXsa9J+eVVpwgU/j9vUFmNS6brsj5s+Cv5tM9V8w2WZZT3MMTudTnEi +ILLimXtdvqw8dv7sPd5syEBHscjd1HTmxp8NWhlxR+FadkghkdYzigxfST52QuqHpAw Vxbs+RoymPPNWSq9Jocw7uPqjkkbe7ZuI2Fy3nuu+h+FVqxf2A0/KC6Szxt0QU/67PkT TS74Sj3xF1k5PgsAnVUTCBd6Fb3LQiUL24xfdamNeeFuFEFZkXYyj1jtANdjo/NagYbU korA==
X-Gm-Message-State: AOAM5336hVS1Ii2KSlOO7qXNEYqFNUuIkE66Kiwu+ur+GLkDB7nP9TnX e8VarDGrhNOdgR1rLrWDmHYHdWzRfmVJ5g==
X-Google-Smtp-Source: ABdhPJzeA4CQNM1eoVNno1wWCzKLyMVqAEPQNn853Rsk9x1poe4F9NXTwg8eHq9+adJg7THnzdvt8w==
X-Received: by 2002:a17:902:56d:b029:d7:c927:2e51 with SMTP id 100-20020a170902056db02900d7c9272e51mr9089604plf.27.1607193459496; Sat, 05 Dec 2020 10:37:39 -0800 (PST)
Received: from mike-mac.lan ( []) by with ESMTPSA id ds24sm5771003pjb.30.2020. for <> (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 05 Dec 2020 10:37:38 -0800 (PST)
References: <20201205182930.5DFDA2900B51@ary.qy>
From: Michael Thomas <>
Message-ID: <>
Date: Sat, 5 Dec 2020 10:37:37 -0800
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.5.0
MIME-Version: 1.0
In-Reply-To: <20201205182930.5DFDA2900B51@ary.qy>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Content-Language: en-US
Archived-At: <>
Subject: Re: [dmarc-ietf] A policy for direct mail flows only, was ARC questions
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: Sat, 05 Dec 2020 18:37:42 -0000

On 12/5/20 10:29 AM, John Levine wrote:
> In article <> you write:
>> mailing list to mailing list mail is very common in GSuite, but maybe we're
>> a special case.
> I dunno how special that case is, but there are lots of cases where mail passes
> through multiple layers of ARC signing mutations.
> I routinely get mail from Microsoft's farm with an ARC seal or two
> that has never been near a mailing list. Any time a MS user sends a
> message to one of my lists, it'll emerge with at least two ARC
> signatures.

Getting multiple signatures from the originating domain doesn't hurt 
anything. It's a little wasteful, but that's it.