It's definitely the best for heavy users. I really only care about performance and Postbox, Mail.app, Thunderbird, Outlook and mutt were all too slow. I haven'

It's definitely the best for heavy users. I really only care about performance and Postbox, Mail.app, Thunderbird, Outlook and mutt were all too slow. I haven't tried Mailbox.app, but it's got some weird Dropbox integration so I wouldn't bother.