Explanation of MAPI, Exchange Web Services (EWS), and Exchange ActiveSync (EAS). Which of these do I need?
There is some confusion over the various types of synchronization options that are available for desktop and mobile email clients and devices. Below are the explanations of each protocol.
MAPI/EWS - Both are protocols introduced by Microsoft for Exchange that are intended for desktop email clients such as Microsoft Outlook. At this time, Microsoft Outlook 2015 for Mac from Office 365, Outlook 2011 for Mac, Apple Mail and eM Client support EWS. MAPI is supported by Outlook 2016 for Windows and above.
EAS - Another Microsoft protocol that is the industry-standard synchronization method for mobile email clients such as iPhones, Samsung Galaxy and Note phones as well as iOS and Android tablets. EAS is also available for use with Windows Mail, People and Calendar and the Outlook client for iPad.