Support for COM Add-ins
Microsoft Outlook allows you to enhance and extend the application using Component Object Model (COM) add-ins. A COM add-in is a dynamic-link library (DLL) that’s specially registered so that it can be loaded by an Office XP application. You can build a COM add-in with a variety of languages, such as Microsoft Visual Basic and Microsoft Visual C++.
Learn more about customizing Outlook using COM add-ins.