If you're stuck in an #Exchange environment (Like I am at work) I can recommend Hiri Mail Client, it's a cross platform Exchange Client (although proprietary) it has been the smoothest use of MSExchange I've had on Linux.
https://www.hiri.com/
@mattmcnutt I use Evolution with EWS instead; libre and doesn't look like an Electron app (yes, I know that one in OP is Python+Qt, but it doesn't even try to look like something native)
@calvin I was using kmail with akonadi EWS (which integrates exhange into KDE PIM), and found it to be a headache to keep running. I am actually really hoping that KDE's Kube mail client will eventually hook into the same EWS package.
Although it is not "native" looking, I actually don't find Hiri to be offensive. It's definitely a good option
@mattmcnutt I'd also like to add that ExQuilla is an option