There was a Linux client I saw a while ago—Spring Mail or something like that?—which first downloaded your email from your provider onto their own servers, then your local client got them from their server. This additional cloud step is what I want to avoid.
Still no html composing, right? It would be a serious contender for many people if it just had that feature... Even though, from my experience, most personal email doesn't really use html...
There is also Mailbird (not FOSS, costs money and has some weird NordVPN-like fake sales, but the app seems somewhat competent) and Mailspring (partly open source but afaik not completely, built with a MacOS-esque UI but works for Windows and Linux as well).
That’s going to be killed off in favor of Outlook in the near future, from what I understand.
If OP is willing to do a bit of extra legwork and somewhat masochistic, then pretty much any Linux-based mail client is fair game with WSL2. The only one I’ve used lately other than Thunderbird is Evolution, but that was just to test a particular distro’s default offering.
And that's why I'm explicitly noting that they're not FOSS, doofus. Besides, if you're using Windows anyway, using its built-in email client is not a huge stretch.
Given people are regularly promoting proprietary trash and being upvoted for it, while people taking a pro-FOSS stance are downvoted, I don't think this is a FOSS community in anything but name anymore.
At the very least I'd have hoped we'd left the childish name calling behind at reddit, but it seems you can't really take the reddit out of the redditor.