Other chapters in this book discuss the messaging technologies that Unity uses; specifically, see Chapter 5. To give you a good idea of how Unity uses these different technologies, they are presented here briefly.
Unity's Messaging Technology
Unity's use of Exchange is based on the Messaging Application Programming Interface (MAPI). The MAPI implementation focuses on accessing subscriber mailboxes to retrieve messages on their behalf, sending messages on their behalf, and notifying subscribers when they receive messages.
The MAPI Profile and System Mailbox
With Exchange, Unity's key to servicing subscribers is through MAPI. That includes its use of a MAPI profile and system mailbox that is used to address messages from outside callers to subscribers of the system. The system mailbox also provides notification services for subscribers by monitoring their mailboxes for new messages and filtering on new voice messages. It basically monitors the state of all messages in a subscriber's mailbox so that it can act upon the state appropriately.
Unity's use of Domino is based on the Notes API; it uses the Lotus Notes client to access the Domino directory and messaging system. Through the Notes client, Unity provides unified messaging services to all subscribers. The implementation is a little different than in the Exchange version. This is largely the result of DUCS, which is in place to provide end-user proxy services for outside callers and to deliver messages to subscribers. The DUCS client provides a media master control for playing back and recording messages.