A policy, associated with a group, controls user subscription to and unsubscription from that group. In one embodiment, there are at least four policies for subscribing/unsubscribing: open, open with filter, control through workflow and closed. An open policy does not restrict subscription or unsubscription....http://www.google.com/patents/US7475151?utm_source=gb-gplus-sharePatent US7475151 - Policies for modifying group membership
