16.8. Microsoft Messaging API (MAPI)The Microsoft Messaging API (MAPI) is, as the name implies, an application programming interface (API) and not a network protocol at all. It is included here because for various reasons, including the uncanny resemblance of its name to "IMAP", it is often mistaken for a mail protocol. MAPI is used on Microsoft operating systems for applications to communicate with messaging systems. It is internal to a single machine; an application uses MAPI to communicate with MAPI drivers, which then communicate with mail and directory servers. A MAPI driver will use whatever protocol it needs to in order to communicate with mail and directory servers. This means that applications that are programmed with MAPI can be used with a variety of email servers without changes, by changing the MAPI drivers.
Knowing that an application uses MAPI does not allow you to predict what protocol will be used to communicate between a client and a server. Instead, you need to know what protocols the MAPI driver is using; usually the easiest way to determine this is to determine what kind of server is being used. Probably the biggest user of MAPI is the Microsoft Exchange client, which is provided with MAPI drivers that use Microsoft RPC to speak to Microsoft Exchange servers.
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