(Mail API) A programming interface from Microsoft that enables a client application to send to and receive mail from Exchange Server or a Microsoft Mail (MS Mail) messaging system. Microsoft applications such as Outlook, the Exchange client and Microsoft Schedule use MAPI. Simple MAPI is an enhanced version of the Common Messaging Calls (CMC) X.400 standard, while Enhanced MAPI adds full calendaring and workgroup capabilities. Collaborative Data Objects (CDO) wraps the Enhanced MAPI library into COM objects (see CDO).