I'm not sure it's worth building an email client that works with Exchange/Office 365 on Linux, when you can use the web interface. Particularly as much of a PITA that trying to use EWS is, and how different it is for on-premise vs Office 365 usage.

It's currently a toss-up whether it's even worth trying to use Outlook on Windows desktops, as much of a buggy, hogging, piece of garbage it is.