I found in the documentation of the "Outlook Mail REST API" (https://msdn.microsoft.com/office/office365/APi/mail-rest-operations) that it applies to "Exchange Online | Office 365 | Hotmail.com | Live.com | MSN.com | Outlook.com | Passport.com".
Does the "Exchange Online" piece relate to the "Corporate Exchange-based email that does not use Office 365" that is mentioned in the table here (https://support.office.com/en-ca/article/Sign-in-to-Outlook-Web-App-e08eb8ac-ac27-49f4-a400-a47311e1ee7e) or are there other options to integrate with on-premises (Microsoft Exchange Server) corporate email?