This policy prevents federated contacts from inviting users to conversations. In addition, it blocks any sesssion (IM, Audio, ...

"This policy prevents federated contacts from inviting users to conversations. In addition, it blocks any sesssion (IM, Audio, Video, Appsharing) from reaching the user from such contacts. This in effect blocks inbound federated traffic from contacts. Audio and Video calls are automatically routed to the user's voicemail   This policy will override any user preference set in the options dialog Personal tab. Otherwise the user can make the choice."