Restricting users on who they can contact?

I’ve heard its possible to restrict users on who they contact, for example they can only contact people in a certain group. Can someone explain how this can be achieved? (not using active directory, groups in spark).

http://www.igniterealtime.org/projects/openfire/plugins/packetfilter/readme.html

Install this plugin and configure it.

LG

Thanks alot, this is exactly what i was looking for