I already have enough trouble with over-paranoid mail system admins.
so do I. which is why I don't want mail being filtered just because
I happen to send mail from a dialup account (or my palm pilot)
with my normal return address.
the mail standards specifically allow the sender to alter the From address,
and you really want return-path / MAIL FROM to point to the place where
the sender will get the nondelivery reports resulting from mail that he
sends. (list mail excepted)
so I don't think it's reasonable to try to restrict which From addresses
or which return-path addresses can come from which MTAs.
Keith