Thunderbird. Free and open source, thus no corporate data collection garbage. Even supports extensions like uBlock Origin and comes with PGP encryption built in. They’ve recently had a major design overhaul as well.

I’d strongly advise against using Spark if you want your emails to remain private.

This is so dumb. I’d rather install an update that bricks the services of a spyware company that I avoid at all costs rather than having an active vulnerability in my OS. Heck, that shouldn’t even be called a bug as it kind of is a feature I actually want.