Jason Snell, at The Sweet Setup:
Because Apple makes it, Mail is for everybody. But it’s not for everybody. Apple designed it to serve the masses, and if you want more–or less–from your email client, Apple Mail may not suit you. Maybe its old-school approach to mail, lifted from classic mail clients like Eudora and NeXTMail, just doesn’t fit the modern emailer. Maybe you want deep links to productivity apps on your Mac that Mail just won’t provide. Or maybe you’re just tired of being in a dysfunctional relationship with Mail.
All told, we looked at nine different challengers to Mail, each of which brings its own clever spin on how to process or display email.