Stephen Satchell has proposed an alternative solution to sender
rewriting.
On Sun, Jan 11, 2004 at 10:41:41PM -0800, Stephen Satchell wrote:
| I have answered some of Wietse's objections to the forwarding question
| by proposing something completely different: the "Forward: " header.
| See my proposal on the PostFix list.
|
| By having the MTA indicate that the message has been forwarded, with
| particulars, using a "Forward:" header line, the reverse traversal
| doesn't require ANY rewriting, yet allows the use of an accurate
| envelope source line.
|
| Forwarded:
| to new-user(_at_)new-domain(_dot_)com
| for this-user(_at_)this-domain(_dot_)com
| by forwarding-server.example.com
| id CD43CAB37
| ; Sat, 10 Jan 2004 15:44:30 -0500 (EST)
|
|
| The server would then be free to use an envelope source address of
| this-user(_at_)this-domain(_dot_)com for the forwarded message. If there is a
| downstream bounce, it would go to the "right" person, the person who
| needs to fix his damn forwarding. The server can generate an optional
| "courtesy bounce" that would merely say that the message was returned to
| an intermediate point, without specifying who or where -- that would
| save on tech support at ISPs, corporate help desks, and hosting
| companies everywhere.
|
| The downside is that the mail server would have to receive at least some
| of the body of the message in order to implement this system.
|
| With SPF, the effect is that a forwarded message would be sent from a
| conforming server with the "correct" envelope source address, so that
| policy checking works properly. The message is unaltered save the extra
| "Forwarded:" line so that the forwarding mail server need do nothing
| special in the normal case. It does have to do some extra processing in
| the case of a bounce, but so be it.
|
| Note the benefit for free: the bounce has a source address of <>, which
| must be accepted by all servers. Because the "Forwarded:" line is
| generated by the server, the server is able to reject bogus bounces if
| the envelope address is not in a domain serviced by the server, AND
| there is no server "Forwarded:" line in the header. Because we already
| know it's a bounce message, we don't "bounce the bounce" and can
| disconnect abruptly if the header doesn't have the "Forwarded:" line.
|
| Feel free to forward this entire message to the mailing list if you
| like. You'll forgive me if I source it from my spamfilter mailing
| address. :)
|
| Stephen Satchell
|
|
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