mapi

MAPI, or Messaging Application Programming Interface, is a Windows programming interface designed by Microsoft to allow email clients to access messaging stores and services. It provides a framework for reading, creating, modifying, and organizing messages, calendars, contacts, and other mailbox data stored on messaging servers such as Microsoft Exchange. MAPI originated in the early days of Exchange and Outlook and exists in several forms, including Extended MAPI and Simple MAPI.

An application that uses MAPI runs within a MAPI session and relies on a MAPI profile to specify the user identity and mailbox to access. The architecture includes MAPI Service Providers, which implement particular data stores and services; and MAPI stores, which represent mailbox data, folders, and public or private items. Transport between a MAPI client and the server traditionally uses RPC-based mechanisms, though modern deployments often employ MAPI over HTTP as the preferred transport.

Outlook for Windows is the primary consumer of MAPI to access Exchange mailboxes. Other software can implement MAPI interfaces directly or via wrappers such as Extended MAPI or Simple MAPI. Over time, Microsoft has expanded messaging access with newer APIs like Graph API for Exchange Online and RESTful services, while MAPI remains in use for on-premises deployments and legacy clients.