I just can’t find a decent email client that looks like it’s from the last 20 years. Geary and Evolution both appear to be pretty modern but something about using Gmail with a Yubikey just doesn’t work and neither of them will connect to my account. Both on Fedora and OpenSUSE. Thunderbird works but it’s so old fashioned and Betterbird doesn’t look much better. What’s everyone else using?
I’m not all in on MS online yet so I can’t help you. We run Exchange on prem. I am the MD of my company and have views about the way forwards (and it won’t involve MS)
The owl plugin for Thunderbird is very good. I have bought a paid subscription to that. Everything works fine with Thunderbird now.