Private messaging with group access rights

I am working on a Community site where it is necessary to have group access control between users. The idea is that they only are allowed to send messages to members of groups they are subscribed to. I wonder if there is already work done on this subject. Does any one know?
Otherwise, I'll start working on a hack, plugin or component to do this.
Thanks

Post edited by: rlustemberg, at: 2006/04/18 14:20

I think it's easy to hack in uddeim, after all, send a message to Administrators is also included. I thank copy an paste a couple of lines would do the trick. I think i'm going to look at it this week

Thanks Lennox, I will follow on your hints
I have been thinking about having the users pm each other through connections, and disallowing all other ways of pm'ing. This site needs a very restricted way in which the users communicate with each other, so using the connection thing will be very acceptable. On the other hand, for the sake of reusability, perhaps a more general approach would be a better idea.
i am new to CB and uddim, so I will need to examin the code thoroughly before I get going...