Re: [dmarc-ietf] Ticket #1 - SPF alignment

Scott Kitterman <sklist@kitterman.com> Tue, 26 January 2021 13:14 UTC

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From: Scott Kitterman <sklist@kitterman.com>
To: dmarc@ietf.org
Date: Tue, 26 Jan 2021 08:14:45 -0500
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Subject: Re: [dmarc-ietf] Ticket #1 - SPF alignment
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On Tuesday, January 26, 2021 6:54:56 AM EST Alessandro Vesely wrote:
> On Mon 25/Jan/2021 22:35:09 +0100 Scott Kitterman wrote:
> > On Monday, January 25, 2021 4:04:33 PM EST Todd Herr wrote:
> >> May I propose that the section labeled "SPF-Authenticated Identifiers" be
> >> rewritten as follows:
> >> 
> >> [...]
> >> 
> >>    The reader should note that SPF alignment checks in DMARC rely solely
> >>    on the RFC5321.MailFrom domain. This differs from section 2.3 of
> >>    [@!RFC7208], which recommends that SPF checks be done on not only the
> >>    "MAIL FROM" but also on a separate check of the "HELO" identity. >
> > 
> > I think this is fine, but there is a subtlety to be aware of.
> > 
> > If you look at RFC 7208 Section 2.4, when Mail From is null,
> > postmaster@HELO is the mail from for SPF purposes.  DMARC really can't
> > change that.
> > 
> > As a result, there are cases where Mail From results actually are derived
> > from HELO and it's unavoidable.
> 
> I doubt that SPF filters report envelope-from=postmaster@HELO; more likely
> they write helo=HELO.  In that case, the paragraph quoted above is
> deceptive.
> > I believe the proposed text is clear enough about not using separate HELO
> > identity results and that's appropriate.
> 
> My filter collects SPF results recorded from an upstream SPF filter.  It
> writes Received-SPF: lines for each identity.  For NDNs, it writes a
> Received-SPF: for the HELO identity only.  Am I allowed to use that result
> for DMARC?

No.  You should only use Mail From results.

Scott K