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

"John R Levine" <johnl@taugh.com> Tue, 08 April 2014 06:28 UTC

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Date: 8 Apr 2014 02:28:15 -0400
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From: "John R Levine" <johnl@taugh.com>
To: "Robin H. Johnson" <robbat2@gentoo.org>
Subject: Re: DMARC: perspectives from a listadmin of large open-source lists
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References: <robbat2-20140408T031810-279861577Z@orbis-terrarum.net> <alpine.BSF.2.00.1404072357400.73388@joyce.lan> <20140408053752.GB2858@orbis-terrarum.net>
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> I think the original scenario you described could be implemented by bad
> players as follows:
> - set up a mailman instance with DMARC support, that forges the XOAR header.
> - Ensure that the mailman outgoing mail passes SPF+DKIM for the domain in question.

Right, except it doesn't even have to be mailman, just spamware that 
creates headers that look like mailman's.  Like I said, if you trust the 
sender to be a real list, deliver its mail.  If you don't, don't.  I don't 
think there are any major conceptual challenges here.

> Those uses shouldn't be considered valid, and NYTimes has already moved
> away from that, at least as of my test 5 minutes ago.

Well, the WSJ does.  This is a perfectly reasonable way to send mail, 
endorsed by decades of practice.

|Date: Tue, 8 Apr 2014 02:24:13
|From: "wsjol@johnlevine.com" <wsjol@johnlevine.com>
|To: johnl@taugh.com
|Subject: WSJ.com - Ukrainian leaders, U.S. slam Russia over new unrest;

The envelope bounce address is <bounces@wsjemail.com>om>, again perfectly 
reasonable.

> By implement DMARC, I meant implement XOAR headers; VERP is too useful

As described above, XOAR is not useful because you can't trust it.

Regards,
John Levine, johnl@taugh.com, Taughannock Networks, Trumansburg NY
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