hello.. fisrt u have to make a user account in the domain ...so u can assign a user access or by ip address... then u have to do make a protocol rules so u can select a protocol msn and msn messenger ...and then assign to a particular user to that rule ...then u will the only the protocol u assign will use by the user if this tip is not work try other tips that u have to search a ports that the yahoo messenger use ..if it is difficult for u to find a ports of yahoo then send me a mail at this address ( dallience@xxxxxxxxxxx )