In general, no two e-mail addresses are alike. There are no hard rules. Nothing is allowed on the net. There are two hundred million people on the net, and some of them are bound to be as crazy as you. A few are even crazier.
Civil law is a different story, of course.
The laws of libel and assault should apply as much to the net as to any other conversational medium. If it's legal there, it's probably legal here. And if it's illegal there, it's probably illegal here, if anyone decides to enforce it.