A more interesting case arises in the sieve notify extension (currently in
draft). Since this for the creation of an entirely new message that can be
sent
right back to same sieve script, it is possible to construct loops where each
time around you're dealing with a completely different message with nothing in
common with its predecessors. This case definitely needs to be looked at
before
notify is standardized.
My suggestion is to keep all Received: header fields. I can't think of
a more effective way to prevent loops.
Michael