Alan DeKok wrote:
Tony Finch <dot(_at_)dotat(_dot_)at> wrote:
I cannot work around this problem: I have no reasonable way of knowing
that this forwarding relationship exists, or if I do know about it I have
no reasonable way of maintaining a list of example.edu's outgoing email
servers in order to whitelist them.
And I don't see why (in the idealogical sense) this would be your
problem. If other sites are forwarding your users messages, then
that's a matter between them and the users. You shouldn't have to be
involved.
Practically, the practice is common, and people resist mightily
changing their habits.
When the sender sends a message to the receiver, the edge of the
receiver´s system in this case would be the forwarder. It is the
responsibility of the receiver to make sure that the steps taken after
the forwarder accepts the mail from the sender´s system are correct.
Therefore in this specific case, the forwarder would have to do
Sender-ID checks in order to protect its users. Therefore, you don´t
have to do anything - it´s the end users that do. In a similar fashion
when a mailing list is involved, it is the responsibility of the list to
do the Sender-ID checks at the edge when it accepts the mail from its
users, and the end users will do their own checks against the list itself.
Yakov