For the Chat Feature, every new message triggers an email to be sent to all chat participants with the text "New Message".

It might be useful to have one single notification email for when the chat is created (on the first message) to make people aware that "hey you've gotta see this).

After the initial notification email, then i'd prefer to have further email notifications turned off by default, and let users enable them, just like notifications for Forum activity (and maybe even on a per-chat-thread-basis).