Perhaps the legal system needs to consider this as case law is established, and the harsh penalties imposed on the published word would be tempered when the comments were made in a private conversation. For the moment, it appears existing libel laws will take precedence and some lawyers are already operating on that basis. I think we should be aware of that we we engage in online discussions. To the best of my understanding, those who post to newsgroups or email lists are indeed open to libel charges if what they post is defamatory. Libel involves false injurious statements that are published.
Publishing means communicating to others besides the one defamed.
Posting to a newsgroup or email list would be publication. That's who the plaintiff would like to sue, of course, because, for one thing, the person posting the message might be anonymous or not to be found, and, for another thing, the online service provider is likely to have deeper pockets.