[Serusers] Parallel forking and reply error

Hi, all I'm implementing a black list, the control access to the gateway and other control policies and I have a problem with the call forking. In case of a call that generates a parallel forking I want the capability to select if accept or refuse the call for each single contact, but if the first reply that I send to the caller is an error message 4xx, the UA caller shuts down the call. What would I have to do to add my reject (caused by my access control policy) to the call forking administration and so reply an error only if all contacts can not be reachable? I'm trying to implement a solution to reply an error only if all the contacts can not be reachable. To do this thing I need to know the number of contacts that the lookup function has found for the request-uri that is arrived ( Is it possible to know if I have a single contact or a parallel forking?) and, if there are more than one contact associated to the sip uri, how can I go to serve the next contact in list without sending a reply for the destinations that I have to block? Any suggestion? Thanks Daniele