[Mailman-Users] DMARC mitigation - was: Templates

JB jebva at yahoo.com
Sat Apr 4 21:10:16 CEST 2015

I can hardly believe I actually followed that whole post start to end!  Thanks Mark.
On Sat, 4/4/15, Mark Sapiro <mark at msapiro.net> wrote:

 Subject: Re: [Mailman-Users] DMARC mitigation - was: Templates
 To: mailman-users at python.org
 Date: Saturday, April 4, 2015, 1:38 PM
 On 04/04/2015 09:59 AM,
 Laura Creighton wrote:
 > ps -- anybody know why all mail I see from
 people on yahoo.com (including JB
 > here)
 arrives to me as from yahoo.com.dmarc.invalid.
 > It very much seems
 to be a python.org thing, but, ah, why is python.org
 > seeing fit to add this stuff?
 DMARC mitigation. Mailman has features for this, but on this
 at least they are turned off. See
 something about DMARC in general and
 Mailman's mitigation features.
 The problem is yahoo.com, aol.com and a few
 other domains publish DMARC
 policies of
 'reject'. For our purposes, this means that a
 message with a
 From: address in one of those
 domains that is not validly DKIM signed by
 that domain will be rejected by a lot of ISPs.
 List transformations will
 break the incoming
 DKIM sig so the only way to get such a message
 accepted by many large ISPs is to munge the
 From: domain in some way.
 See the archives of this list from last April
 for much
 discussion of this.
 Mailman's From: address
 munging will replace, e.g.
 From: Mark <mark_sapiro at yahoo.com>
 with, e.g.
 From: Mark via Mailman-Users <mailman-users at python.org>
 and add the original From: to
 Reply-To:, but that doesn't happen with
 python.org mailing lists because the incoming
 MTA at mail.python.org
 deals with this
 differently by just appending .dmarc.invalid to From:
 addresses @yahoo.com, @aol.com and a couple of
 other domains.
 Some people
 think this approach is less disruptive than Mailman's
 way -
 i.e. users when replying are astute
 enough to just remove the
 .dmarc.invalid, or
 if not, maybe they'll figure it out after seeing the
 bounce DSN.
 Mark Sapiro <mark at msapiro.net> 
       The highway is for gamblers,
 Francisco Bay Area, California    better use your sense -
 B. Dylan
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