There are many possible extensions that you can program to work with Microsoft Exchange. These extensions generally fall into four categories:
| Extension type | Description |
|---|---|
| Command extensions | Add new commands to the client's menus and toolbar, or replace the behavior of existing commands and toolbar buttons. For example, you can add commands that are specific to certain folders or selected message types. See Command Extensions. |
| Event extensions | Invoke custom behavior to handle events such as the arrival of new messages, reading and writing messages, sending messages, reading and writing attached files and selection changes in a window. See Event Extensions. |
| Property sheet extensions | Add custom property sheet pages to an object's properties dialog box, enabling users or administrators to view or edit custom message properties. See Property Sheet Extensions. |
| Advanced criteria extensions | Implement your own custom advanced criteria dialog boxes to be used when searching for messages in the information store. This is useful when you want to enable users to search for custom message properties. See Advanced Criteria Extensions. |