Filtering a user in MUC

Hello

How can I create a rule to filter a drop one specific users packets in a group chat. My server receives packets from the rooms jabber ID. There are users in the room fro different domains. Real sender1s jabber id is in the resource part of the source address but not full jabber id , just user part. domain part is missing. SO if it is possible to attach the full jabber id to the source address of the MUC message then we can write a rule for that user. otherwise we should hope that there is no other user with the same username in the room. Is there a solution for that ?