What is the difference between Outlook MAPI and Exchange Web Services (EWS)?

Outlook MAPI is a set of interfaces used to access resources within the Outlook client, such as reading emails from the local .ost file. In contrast, [Exchange Web Service (EWS) Development Guide](/news/exchange-web-service-ews-development-guide) is designed to access resources directly from the Exchange server. MAPI requires the Outlook client to be installed, while EWS does not depend on a local Outlook installation.