Re: DMARC: perspectives from a listadmin of large open-source lists

Sabahattin Gucukoglu <> Tue, 15 April 2014 23:15 UTC

Return-Path: <>
Received: from localhost ( []) by (Postfix) with ESMTP id CC2441A0062 for <>; Tue, 15 Apr 2014 16:15:04 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -4.201
X-Spam-Status: No, score=-4.201 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, SPF_PASS=-0.001] autolearn=ham
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id fYXCvW2Z9jNu for <>; Tue, 15 Apr 2014 16:15:00 -0700 (PDT)
Received: from ( []) by (Postfix) with ESMTP id 318511A0059 for <>; Tue, 15 Apr 2014 16:15:00 -0700 (PDT)
MIME-version: 1.0
Content-transfer-encoding: 7BIT
Content-type: text/plain; CHARSET=US-ASCII
Received: from [] ( []) by (Oracle Communications Messaging Server 7u4-27.08( 64bit (built Aug 22 2013)) with ESMTPSA id <> for; Tue, 15 Apr 2014 23:14:50 +0000 (GMT)
Subject: Re: DMARC: perspectives from a listadmin of large open-source lists
From: Sabahattin Gucukoglu <>
In-reply-to: <>
Date: Wed, 16 Apr 2014 00:14:47 +0100
Message-id: <>
References: <20140414024956.26078.qmail@joyce.lan> <> <alpine.BSF.2.00.1404132327560.26258@joyce.lan> <> <alpine.BSF.2.00.1404132346420.26386@joyce.lan> <> <> <> <> <>
To: Pete Resnick <>
X-Mailer: Apple Mail (2.1510)
X-CLX-Spam: false
X-CLX-Score: 1011
X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.11.96, 1.0.14, 0.0.0000 definitions=2014-04-15_03:2014-04-15, 2014-04-15, 1970-01-01 signatures=0
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 suspectscore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=7.0.1-1402240000 definitions=main-1404150387
Cc: John C Klensin <>, Dave Crocker <>, " list" <>
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: IETF-Discussion <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Tue, 15 Apr 2014 23:15:05 -0000

On 15 Apr 2014, at 23:20, Pete Resnick <> wrote:
> On 4/14/14 9:23 AM, Dave Crocker wrote:
>> Mediators, like mailing lists, take final delivery and post a new message.  In formal terms, it's legitimate for them to create a different rfc5322.From field, including one that looks like some sort of 'rewrite' of the one used by the original author.
> It's legitimate for a mailing list to rewrite the author, but it would be wrong. :-)
> More seriously: If the mailing list wishes to express that I am the author of *this message*, then I belong in the "From:" field. That differs semantically from forwarding a message authored by me; then the list is saying that the list is the author, and it is simply quoting me, but that the list is the entity that should be considered to have written the message. For most mailing lists, that seems like the wrong semantics to try to convey.
> There should be a mechanism for an author to send a message to a mailing list, granting the mailing list permission to redistribute that message, and have that permission conveyed to the mailing list recipient such that when the mailing list recipient receives the message, they can assure themselves that the originating domain is OK with that redistribution. Sounds like some protocol which could be written.
> (If the originating domain is expressly *not* OK with the redistribution, the mailing list should bounce the message back to the author saying as much.)

That suffers the same problems as X-O-A-R: you have to know when to trust the intermediate.  In the absence of that knowledge, any message transformation is invisible to the recipient, and potentially malicious.  You would have to invent a scheme for identifying transformations, so users could verify them against the original sender's signature.

DMARC has put *ALL* the trust into the From: field.  That is very unfortunate, but it seems to be the DMARC peoples' idea of a foolproof, user-visible identifier.