Office Programming Models

Beside VSTO (Visual Studio for Office) and PIA (Primary Interop Assemblies) for Office 2003/2007, there are two additional older technologies to program against MAPI stores:

1. Extended MAPI (Messaging Application Program Interface) is set of functions that can be used to create MAPI enabled applications. Extended MAPI (or MAPI 1.0) allows complete control over the messaging system on the client computer, creation and management of messages, management of the client mailbox, service providers, and so forth. Extended MAPI is programming using C or C++.
2. CDO (Collaboration Data Objects) is a COM wrapper of the MAPI library and can be called from any development language that supports automation. CDO implements most but not all MAPI functionality.

Both of them provide a way to read and write more properties for MAPI store and items than PIA and to accomplish more tasks that using VSTO so sometimes they are the only way to do something. But VSTO 3.0 and PIA for Office 2007 provides more options to make custom MAPI items and stores so there is less need for using additional technologies.