I don't think I've ever been "in love" with Postbox, but it's always done email reliably well that I never had to think about it. Plus, it never tried to be anything more than an email client - I never had to worry about it trying to be a "business workflow productivity tool" or anything, it just did email decently.
eM looks like exactly the kind of tool I _don't_ want.
It used to be more important to me that my email client also support Windows, but way less so now. (My Windows machine is just a gaming machine, and that's even only just until Windows 10 stops being actually usable for gaming.)
What's everyone favourite Mac "just an email client" email client?