if (uid == null) return false;
Destination d = (Destination)destinationList.get(uid);
if (d == null) return false;
PacketReference ref = (PacketReference)d.destMessages.get(id);
if (ref == null) return false;
return (ref.checkLock(false) == null);
}
/**
* adds information on the new message to the globals tables.
* It may or may not change the size (since the size may