The decision to allow priority requests may not be based on
identifying trusted and authenticated parties at all.
understood. but if this turns out to be the usual policy, we will
have added a fair amount of useless complexity to the mail system.
I don't think we should dictate the policy by which sites choose
to honor a priority request, but I do think we have to make sure
that adequate authentication mechanisms exist so that sites that
want to prevent abuse of priority (while still being able to extend
that privlege it to those for whom they want to) can do so.