The Boston ruling about email might apply to http caches
(non-transparent ones) and possibly OPES processors acting on behalf
of the recipient. I don't think it has much to do with protocols, but
it has a lot to do with storing message copies.
The article implies that if the content is stored as a service to the
user, then it is not protected under wiretap law. It sounds as though
the SMTP store-and-forward phase is still protected until it hits the
ISP that is acting on behalf of the recipient. At that point any
message copies are assumed to be a storage service for the recipient.
But, I'm not a lawyer and have based my opinion entirely on the
article, and that article is written by someone who is neither a
lawyer nor an Internet expert.
Hilarie