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?
Thunderbird is working on enabling exchange, and meanwhile you can combine it with TBSync plus its provider for exchange AcriveSync extensions. And given TB hadn’t care so far about tray, to at least avoid TB dying by mistake, you can also add Minimize on Close extension. Mail would still be IMap, so it’ll work as long as the outlook provider enables IMap support, but for the company I work it’s enabled. But such support is coming up on TB. Not sure if its solution would be 100% open source, but I hope it is, otherwise, I’m not sure if everyone will want to have a blob proprietary binary inside TB…