In the meantime, Evolution has had EWS support for years… no Rust involved.

Radicale. Not the fastest, but has worked for years.

I use Evolution with the o365 account at work. All one needs is the EWS plugin and the company tenant ID. Evolution then pretends to be a generic MS Office app, using a well-known app ID. oauth2 works just fine.

I’ve been using Miniflux for a few years now, no complaints. Mostly with an iOS-based Reeder app, occasionally with the Web frontend.

Orion doesn’t make the list?

WPS Office and FreeOffice. Each with their own caveats, but one just might work for you.