A system built into MicrosoftWindows that enables different e-mailapplications to work together to distribute mail. As long as the applications are MAPI-enabled, they can share messages with each other. MAPI has a history that might cause confusion due to the fact that there are two very different kinds of MAPI. First, in the days of Microsoft Mail (MS-Mail), there was MAPI. It was an API in C that allowed programmable access to the features of Microsoft Mail. Nowadays, that version is called "Simple MAPI."
The second MAPI is a COM/OLE-based set of interfaces of rather high complexity, sometimes called "Extended MAPI" (or XMAPI). Extended MAPI actually includes Simple MAPI, for compatibility with older software. It also includes OLE Messaging, which is a set of OLE Automation interfaces to messaging, for use in Visual Basic and the like.