MAPI uses functions loosely based on the X.400 XAPIA standard. It includes facilities to access message transports, message stores, and directories. While Simple MAPI is a subset of 12 functions which enable developers to add basic messaging functionality, Extended MAPI allows complete control over the messaging system on the client computer. This includes creation and management of messages, plus management of the client mailbox, and service providers. Simple MAPI is included with Microsoft Windows as part of Outlook Express/Windows Mail while the full Extended MAPI is included with Office Outlook and Exchange. In addition to the Extended MAPI client interface, programming calls can be made indirectly through the Simple MAPI API client interface, through the Common Messaging Calls API client interface, or by the object-based ''
interfaceThe full Extended MAPI interface is required for interfacing messaging-based services to client applications such as Outlook. For example, several non-Microsoft e-mail server product vendors created "MAPI service providers" to allow their products to be accessed via Outlook. Notable examples include Axigen Mail Server, Kerio Connect, Scalix, Zimbra, HP OpenMail, IBM Lotus Notes, Zarafa/Kopano, and Bynari. MAPI also had a service provider interface of sorts. Microsoft used this to interface MS Mail to an email system based on Xenix, for internal use. Extended MAPI is the main e-mail data access method used by Outlook, to interface to Microsoft Exchange, via MAPI service providers shipped with Outlook.
MAPI/RPC protocol details
Microsoft has released full details of the MAPI/RPC protocol since August 2007. "MAPI protocol" is a colloquial name for the MAPI/RPC. At times, Microsoft has also called it "Exchange RPC" and "Outlook-Exchange Transport Protocol". Microsoft provides a sample MAPI/RPC-based application called MFCMAPI to assist developers. It is also widely used as a diagnostics tool by both developers and Microsoft Exchange administrators.
MAPI over HTTP
The original implementation was designed for use on a local network, or LAN. The "Outlook Anywhere" feature extended this to an external Internet-facing interface but MAPI/HTTP, introduced in 2014 with Exchange 2013 SP1 replaced this with a more 'normal' HTTP-based stack.
Reimplementations
Several open-source software projects have started working on implementing MAPI libraries, including:
The OpenMapi project had a C# implementation.
Kopano Groupware Core has a C++2011 implementation called "mapi4linux", which offers an API that is source-backwards-compatible with the Messaging API. Kopano GWC comes with a connector for the Zarafa/Kopano-based SOAP/HTTP transport.
OpenChange has a "libmapi" component written in C that only partially resembles MAPI.
The OpenChange subproject Evolution-MAPI is a connector for Exchange implementing the MAPI/RPC transport.
