A system and method for interfacing unified message processing systems with legacy voice mail, e-mail and facsimile systems, located behind corporate firewalls. The system includes a unified message server, a proxy interface and a message protocol converter. The proxy interface is configured to access the legacy system in response to a request from a unified message server. Messages stored on the legacy system are converted by a protocol converter to a predetermined format compatible with the unified message server. The converted messages are then transferred to a unified message server which is capable of providing messages from different messaging system, such as voice mail, e-mail and facsimile to users in a predetermined format. The invention permits enterprise wide communication systems to provide unified messaging without abandoning pre-existing legacy messaging system.