[otrs] Stopping certain email notifications being sent out to clients

Hi, I have created a separate closed state that signifies that a call has been closed but has not been billed for. When a call is put in this state all I have to do is run a search filter on the state and I get a list of what calls I have to bill clients for. The downside of this is that the client gets two closed email notifications i.e. one for my closed not billed state and one for closed successful. I would prefer that the client would receive one email notification on either of states. Is this possible or is there a better way of accomplishing what I am after. OTRS version is 1.31 on RH based distro TIA