You don't interact with your iPhone in the same way that you use your Mac, so why should your mobile email app act like it belongs on your desktop? That's the idea behing Mail Ninja for the iPhone. It uses swipe gestures to reply, delete and archive messages, supports multiple accounts, includes a unified mailbox, offers Push notifications, and even includes a left-handed interface option. Mail Ninja supports, IMAP, Gmail, iCloud email, Yahoo! and AOL, and is available through Apple's iTunes-based App Store for US$2.99.
Check It Out: Swipe through Email with Mail Ninja