Mailing List Archive

Chris Murton wrote:

> Could someone please confirm exactly which headers libspf
> looks against to check against it's TXT records?

Sorry, I don't have the sources. But the idea is to check
mail as early as possible, in the SMTP session at the time
of the MAIL FROM:<what@ever.example>. Normally that's the
2nd step after the HELO resp. EHLO.

> Is it just the last "handling MTA" or does it look back
> further?

The MAIL FROM corresponds to the Return-Path: header content.
If that's empty (in a bounce) the domain in the HELO is used.

Translated to headers (after delivery): If you get an empty
Return-Path: you _might_ be able to find the HELO domain in
the topmost Received: header.

I have no idea about the libspf API, but it's quite possible
that there is essentially one function expecting an IP and an
address (resp. only a domain), returning PASS, FAIL, SOFTFAIL,
or DONTKNOW.

The IP is the IP of the client in an SMTP session. Translated
to headers you _might_ be able to find this IP in the topmost
Received: header. But that depends on your mailer and other
factors, e.g. if you got the mail via your backup MX, then the
2nd Received: header might be relevant (counted top down).

Check out <http://spf.pobox.com/why.html> with a nice SPF Web
interface.
Bye, Frank


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On Jun 7, 2004, at 3:01 AM, Chris Murton wrote:
>
> Could someone please confirm exactly which headers libspf looks
> against to
> check against it's TXT records? Is it just the last "handling MTA" or
> does
> it look back further?

libspf does NOT look at any headers. It looks at the "envelope FROM"
(not the "header From") which is not necessarily represented in any
header, though some receiving mail system might add a copy of it into
the header Return-Path.

The envelope FROM is where mail systems send delivery error reports to.
>
-j
--
Jeffrey Goldberg
Jeffrey@goldmark.org http://www.goldmark.org/jeff/

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