Re: [ietf-smtp] RFC 8601, clarification needed

John Levine <johnl@taugh.com> Sun, 23 May 2021 17:54 UTC

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Date: 23 May 2021 13:53:54 -0400
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From: "John Levine" <johnl@taugh.com>
To: ietf-smtp@ietf.org
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Subject: Re: [ietf-smtp] RFC 8601, clarification needed
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It appears that David Bürgin <dbuergin@gluet.ch> said:
>1)
>
>Authentication-Results: mail.example.org; spf=pass smtp.mailfrom=example.com
>Authentication-Results: mail.example.org; spf=pass smtp.helo=mail.example.com

That is wrong.  One A-R per pass through the MTA, please.


>Authentication-Results: mail.example.org;
>  spf=pass smtp.helo=mail.example.com;
>  spf=pass smtp.mailfrom=example.com

You can do that if you want.

>A subsequent component could then use these results as input to some
>spam score, for example.

You could, although in practice the HELO check doesn't tell you anything useful
except when it's used as a fallback due to a null MAIL FROM.  The useful HELO
check is to see if it exists at all, with a nonexistent one being a close to 100%
accurate spam signal.  But if it doesn't exist, there is no SPF record so SPF
tells you nothing.

R's,
John