As you aware, Office 365 and Exchange Online provide a new way to work with email, calendars, and contacts. The Mail, Calendar, and Contact REST APIs provide a powerful, easy-to-use way to access and manipulate Exchange data.
In this video, you will see Venkat, Principal Program Manager lead will walk you through how to use Microsoft Graph to reach on-premises and cloud users of hybrid Exchange 2016 deployments, in addition to Office 365 and Outlook.com. It’ll discuss how your application can handle versions of servers on-premises and in the cloud, and how on-premises Exchange 2016 is set up to support Microsoft Graph and OAuth.
For more info about related documentation, you can get it started at http://graph.microsoft.io/en-us/docs/overview/hybrid_rest_support
Hope this helps.