On Tue, 7 Dec 2004, Richard Bang wrote:
The optimum solution:
Forwarders don't, they simple tell the sender what address to use, the
sending MTA then uses the new address. If it cannot send, it can bounce to
the author with a sensible message:
That is good in theory but
1. There is no redirect to different server command in SMTP right now
2. Some people do not want to tell what address they are actually using
(they expose to the world their external forwarding address but may
want to keep their internal address hidden and spam-free and use it
only to communicate with their close friends)
3. In some cases we may have situation A->(B->C)->F where B & C are on
the same network and B is network gateway and C is real mail server
which knows where to redirect mail to. So during A->B session B
can not tell if mail needs to be redirected, nor can it tell A to
contact C because C is behind firewall, but once email got to B
it does not make any difference if B sends mail to F or if C does,
both of those are not on the origin network and would fail SPF.
--
William Leibzon
Elan Networks
william(_at_)elan(_dot_)net