I do, backed by mbsync and notmuch. I've tried most email clients and aerc is what's stuck around for the past few years.

If you're looking for something more graphical/visual, Asteroid's worth a try, too.

I do, with mbsync for offline sync. It is great, also with the git email workflow! The author (Drew Devault) has a few videos showing how to use it with git that got me into it.