Re: What I've been wondering about the DMARC problem

"John Levine" <johnl@taugh.com> Mon, 21 April 2014 19:53 UTC

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Date: 21 Apr 2014 19:53:08 -0000
Message-ID: <20140421195308.28955.qmail@joyce.lan>
From: "John Levine" <johnl@taugh.com>
To: ietf@ietf.org
Subject: Re: What I've been wondering about the DMARC problem
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>> As such, the ability to reply to the RFC5322.From tells you almost nothing
>> about its legitimacy. ...

>I seem to recall common use of From: field validation back when that
>capability was introduced into open source sendmail as an anti-spam tactic,
>though it was never supported by the vendor directly.  Maybe it's less
>common now.

If people start rejecting because .INVALID is on the From: line, it
is the work of a moment to adjust it to something like this:

 From: Marissa <marissa@yahoo.com.not.sp.am>

and the work of about three moments to spin up a fake MTA that accepts
any RCPT TO and rejects at DATA.  Or I suppose it could just be an
open relay.  

This of course trains people to be phished, by telling them that
<security@paypal.com.some.thing> is the same as <security@paypal.com>om>.

R's,
John