Depending on the age of your system, would would either use as atrieouellette stated, the Call Director for a mailbox, or if an older system you set it up as the Automated Receptionist... This involves changes in the Line Group (to answer as Receptionist) and configuration of the Automated Receptionist. Unfortunately it has been so long since I have done this way, probably over 15 years, that I forget how to do it... I want to say it is in Off-Line Configuration.