About: Mailbox Accessing APIs
These APIs are used to access folders and items inside mailbox and public folder stores. These are the APIs used to create mail client applications. They have varying levels of business logic available - not all APIs have objects for working with specialized item types like contacts, appointments, tasks, etc. These APIs do not do administrative tasks and do not send email directly by SMTP.
APIs
About: Office 365 REST APIs for Exchange
https://blogs.msdn.com/b/webdav_101/archive/2015/05/18/about-365-rest-apis.aspx
About: Exchange Web Services (EWS)
https://blogs.msdn.com/b/webdav_101/archive/2015/05/03/getting-started-with-ews.aspx
About: Outlook Object Model (OOM)
https://blogs.msdn.com/b/webdav_101/archive/2015/05/18/about-outlook-object-model-oom.aspx
About: Extended MAPI
https://blogs.msdn.com/b/webdav_101/archive/2015/05/18/about-extended-mapi.aspx
About: Exchange Server ActiveSync (EAS)
https://blogs.msdn.com/b/webdav_101/archive/2015/06/01/about-exchange-server-activesync-eas.aspx
Old APIs:
About: CDO 1.21
https://blogs.msdn.com/b/webdav_101/archive/2015/05/18/about-cdo-1-21.aspx
About: WebDAV
https://blogs.msdn.com/b/webdav_101/archive/2015/05/18/about-webdav.aspx
Avoid these:
HOWTO: Read unmounted Exchange EDB files.
https://blogs.msdn.com/b/webdav_101/archive/2008/09/03/howto-read-unmounted-exchange-edb-files.aspx
Directly accessing Exchange database files is NOT supported. There are specific supported APIs for accessing data.
"Enhancing Exchange" via unsupported methods.
https://blogs.msdn.com/b/webdav_101/archive/2013/06/13/quot-enhancing-exchange-quot-via-unsupported-methods.aspx
Also see:
About: Messaging APIs
https://blogs.msdn.com/b/webdav_101/archive/2015/08/07/about-messaging-apis.aspx