Messaging

When Microsoft Exchange Server sends a message, it relies on the MAPI subsystem to direct client requests to one or more transport-service providers.

MAPI defines three types of transport-service providers:

• Message store providers, which supply message storage, organization, and retrieval facilities for a messaging system.
• Address book providers, which supply message addressing and distribution list facilities to the messaging client.
• Messaging transport providers, which move messages between messaging clients.

When a message is sent from a client application, MAPI.DLL responds to the common mail call (CMC) or MAPI call. MAPI then routes the messages to the appropriate message store and address book service provider.

The Microsoft Exchange Server information store offers more functionality than many other MAPI message stores. For example, replication services are part of the Microsoft Exchange Server information store and add new functionality that is then available to MAPI applications. The replicated storage model allows the Microsoft Exchange Server information store to distribute information within an organization or beyond its boundaries without requiring users to know the location of the folders containing the information.

For detailed information about messaging within Microsoft Exchange Server and about MAPI, see the "Database and Messaging Services" section of the Microsoft Platform SDK.