[Mailman-Users] DMARC hack

Mark Sapiro mark at msapiro.net
Mon May 25 02:40:12 CEST 2015

On 05/24/2015 03:19 PM, Allan Hansen wrote:
> $ host -t TXT _dmarc.btopenworld.com
> _dmarc.btopenworld.com descriptive text "v=DMARC1\; p=none\; fo=1\; rua=mailto:dmarcagg at btinternet.com, mailto:dmarc_agg at auth.returnpath.net\;"

The domain publishes DMARC p=none. Thus, no ISP should treat a message
From: someone at btopenworld.com any differently than the same message
From: someone at elsewhere.com.

> Here is the reject notice:
> Final-Recipient: rfc822; subscriber at aol.com
> Original-Recipient: rfc822;subscriber at aol.com
> Action: failed
> Status: 5.2.1
> Remote-MTA: dns; mailin-04.mx.aol.com
> Diagnostic-Code: smtp; 521 5.2.1 :  AOL will not accept delivery of this
>    message.

I see this exact rejection reliably from AOL. When an AOL user posts to
a list, the list post sent back to that user is rejected in this way,
even though AOL accepts the same post for delivery to other AOL users.

I have experimented with this using my own AOL address to send and
reflecting various versions of the message back. I munged a lot of
headers including I think Message-Id:, and I always got rejected. I gave
up trying to figure out what AOL is looking at, but this reject occurs
to list posts from aol.com, even though the From: is munged to the list

In any case, that's not the reject reason uses for a reject due to DMARC

Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan

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