At any rate, the 1978 ECPA seems to give fairly broad options to ISPs
for administrative purposes.
Cubby v Compuserve also seems to side strongly on the side of ISPs vis
a vis protecting them from narrow claims of being "publishers".
True, but the question will be raised whether this is simply administrative,
or they are blocking messages based on content the ISP deems to be
objectionable simply needs the right test case before some trial lawyer will
give it a run. Once you start to say a user can see this, but not that, you
are entering the land of being a publisher.