spf-discuss
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Re: Problem with SID

2005-06-23 14:29:54
Stuart D. Gathman writes:
This conversation hinges on the distinction between relaying - passing 
a message on to another MTA unchanged except maybe to
add a Received header, and "resending" - sending on a message
with this MTAs domain in the MAIL FROM, and possibly changing
or adding multiple headers.

Some of us, like Roger are using "forward" to mean "relay".
Others of us are using "forward" to mean "resend".

Traditionally, "forwarding" has meant something in between relaying
and resending: changing the envelope "To" address without changing the
envelope "from" address.

Using my earlier example, mail would arrive here as mail
        JaneDoe(_at_)aol(_dot_)com --> JohnBuck(_at_)example(_dot_)com
and leave as mail
        JaneDoe(_at_)aol(_dot_)com --> JohnBuck(_at_)BigIsp(_dot_)com

Among other things, forwarding means DSNs go to the right place, in
this example to JaneDoe(_at_)aol(_dot_)com(_dot_)  Forwarding with the envelope 
intact
is (or at least has been) considered a premium service compared to
resending, somewhat like direct connection vs. proxying.

1. SPF does not break resending a message.

2. SPF does not break relaying, ...

True enough, but SPF does break forwarding.  Forwarders have to become
resenders.

This causes problems of its own.  For example, some of my users have
opted out of my anti-spam filtering, so at their request I resend tons
of spam to them.  The providers they have me forward ... er, resend to
see all this junk coming from my domain.

There's a commercial anti-spam package that has an option to regard
all mail with "=" character in the MAILFROM as spam.  SRS rewriting
uses "=" as a separator, so sites running this anti-spam package
reject all SRS-rewritten mail if they've enabled the option.

Other edge case may turn up.  They are unlikely to make me abandon SPF
and SRS, but they are real problems that do have to be dealt with.

--
Dick St.Peters, stpeters(_at_)NetHeaven(_dot_)com 
Gatekeeper, NetHeaven, Saratoga Springs, NY


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