@tbaugh has mentioned a few times, that while he’d like to make the switch to more open source and linux in his daily routine, his work email is from Exchange (Microsoft), and it’s hard to find a good client for Exchange that’s open source, and LInux friendly.
Here are a couple I’ve found recently.
https://www.nylas.com/ Nylas N1 is an interesting looking one. While it doesn’t have a built in calendar it does look like it has a clean interface for email. It’s web-based, but installs locally and from what I can tell should work on any desktop platform.
Evolution Mail by Gnome is another one that touts the ability to work with Exchange, and does have the built in calendar, contacts, tasks, and so on, that one would look for in an Outlook type application. It has a nice, clean interface, and appears to have come a long way in the last few years. It might be worth a look as a solid option.