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Re: [dmarc-ietf] Nitpicky questions about DMARC record syntax

"John Levine" <johnl@taugh.com> Thu, 17 January 2019 16:53 UTC

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From: John Levine <johnl@taugh.com>
To: dmarc@ietf.org
Cc: gtaylor@tnetconsulting.net
In-Reply-To: <43ae9a84-75e3-1292-d3f4-68f3a74458a3@spamtrap.tnetconsulting.net>
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Archived-At: <https://mailarchive.ietf.org/arch/msg/dmarc/I3HO1oPYFxDPgWwfjC70wHoNQ7o>
Subject: Re: [dmarc-ietf] Nitpicky questions about DMARC record syntax
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In article <43ae9a84-75e3-1292-d3f4-68f3a74458a3@spamtrap.tnetconsulting.net> you write:
>However I still feel like /requiring/ exact case is contrary to the idea 
>of "Be liberal in what you accept and conservative in what you send.".

Yup.  See

https://datatracker.ietf.org/doc/html/draft-iab-protocol-maintenance

a/k/a "Postel was wrong".

>I don't see any security implications in accepting the following:
>
>dmarc-version = ("v" / "V") *WSP "=" *WSP ("D" / "d") ("M" / "m") ("A" / 
>"a") ("R" / "r") ("C" / "c") "1"

Please see the previous several dozen messages, particularly the one
about the brown M&M's.  If you know that someone didn't read the spec,
you can only guess what else they got wrong, and you're not doing
anyone a favor by doing that.

>I agree that this is contrary to the letter of the specification. 
>However I think it is completely within the spirit.  Especially when 
>dealing with DNS data which is inherently / invariable human entered.

Once again, please try not to assume that everyone's experience is the
same as yours.  On my DNS server, the DMARC records are generated
automatically when I add a new mail domain and their syntax is
correct.  (Or every DMARC record is wrong, but I would notice that
pretty soon.)  On the large systems which these days host most mail
it's hard to see how they could do it manually.

R's,
John

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