Building a Client Application

A client application is a program that runs on a user’s computer, communicates with Microsoft Exchange Server, and is controlled through a user interface. Most client applications interact with Microsoft Exchange Server by retrieving data from the information store, placing information in a public folder, or manipulating messages to be sent or posted. A third-party client application may perform actions similar to those of the existing Microsoft Exchange Client, or it may supply new functionality.

It is not necessary for a client application to be accompanied by a server application. For example, a hypothetical application could be started by double-clicking its icon like any other Windows application. The application could then log on to Microsoft Exchange Server, gather information from a public folder, and display the information. One of this application’s tasks may be to check the Windows NT Registry and determine the correct information to gather and display for a particular user.

Microsoft Exchange Server can support client applications that run independently — whether or not the Microsoft Exchange Client is running at the same time. Such client applications are set up to operate directly through MAPI and to connect their logons to an active Microsoft Exchange Server application that is MAPI-compliant. The application can then interact with information in the Microsoft Exchange Server information store and manipulate information stored and distributed by Microsoft Exchange Server.

The following factors may indicate that a standalone client application is appropriate:

• Your application presents users with a different user interface than Microsoft Exchange Clients, but provides access to Microsoft Exchange Server information.
• Your application presents Microsoft Exchange Server information in a different way than users normally encounter. In this respect, Microsoft Schedule+ is a good example of a client application. Scheduling information is stored and distributed through replication by Microsoft Exchange Server, but the context in which it is presented differs from Microsoft Exchange Clients.