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[spf-discuss] Re: "pretend" MAIL FROM = forwarder white-listing (if forwarder has SPF record)

2007-03-14 03:18:51
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Stuart D. Gathman wrote:
Suppose MyForwarder is your alias forwarder.  They do not use SRS.
However, they *do* control their own myforwarder.com domain (where your
forwarded address resides) with an SPF record.  So, when you get mail,
the MAIL FROM will be

MAIL FROM: <joe(_at_)randomdomain(_dot_)com>

*But*, before check SPF for randomdomain.com, you check SPF as if the
MAIL FROM was:

MAIL FROM: <postmaster(_at_)myforwarder(_dot_)com>

instead.

If that gets a pass, then you know the mail was forwarded (and SPF
checking on the actual MAIL FROM is useless).

If myforwarder.com doesn't actually have an SPF record, then some
SPF libraries (e.g. pyspf) will allow you to supply a substitute that
you figure out and maintain yourself.

That's sort of what forwarder white-listing AKA TENBOX intends to do, 
except that it covers only the case where the forwarder does have a 
(complete) SPF record.  The other case (forwarder neither has an SPF 
record nor does do SRS) still needs to be solved.

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