BuddyPress private messaging works like internal site email. Members can message people on their friends list as well as forward and reply to received messages.
Each member will have their own individual Inbox, Sentbox, and Drafts folder. They will be notified of new messages by a new message count on their Messaging tab as well as email notifications if enabled.
Private messaging will utilize the TinyMCE editor built into WordPress so that HTML formatted messages can be sent.
Sending of messages by group administrators and to multiple friends, as well as site wide messages by an administrator are also in consideration.