can you explain more about the configuration of the Unity Connection?! Is there a exchange integration (MAPI) or is the delivery to Email via IMAP only ?
Also did you have define a Call Forward Information in CUCM (HuntPilot). I mean you have to give us more information about your configuration.
Just for example! You can set a Call Forward no Answer in CUCM to 999X ... SIP Trunk to Unity Connection Matching RoutePattern 999X
In CUC you cofigure an Forward Filter with called party 999X -> Go to System Handler and Configure your desired Solution....perhabs a Message like a "small" IVR .... pressing 1 Go ... Pressing 2 ... Go.... and so on....