Re: [Asrg] Re: Why SPF? (was: Anti-spam laws do work, FYI. There's proof.)

["Alan DeKok" <aland at ox.org>]

Dave Crocker <dcrocker at brandenburg.com> wrote:
>  spf "authorizes" MTAs to carry traffic "on behalf of" the identified
>  RFC2822.sender (as derived into RFC2821.mailfrom).

  I would say it authorizes MTA's to *originate* SMTP sessions.  This
is very different than "carrying" traffic.

>  this is like authorizing IP routers to carry particular datagrams,
>  based on the author of the datagram payload.

  That's a false analogy, based on wording that MTA's "carry" traffic.

  You're trying to compare an intermediate host (router) which
forwards traffic unchanged, with an MTA which is originating traffic.
The two situations are different, and incomparable.

  In the cases where MTA's are "forwarding" messages, I would argue
that their function is *very* different from an IP forwarder.  MTA
"forwarders" are closer to application-layer gateways, which transform
one input stream into a related output stream.  In that regard,
they're operating more like a NAT box.

  And in a NAT box, it's reasonable to have rules saying "IP addresses
on the inside MUST be in a certain range, or they're not forwarded".

  Alan DeKok.

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