Outlook for iOS
Over at our sister site, The Sweet Setup, Outlook was picked as the best third party email app for iOS.
Email apps are highly personal. Everyone manages their email differently. For some, it's a to-do list. For others, it's a temporary holding place until emails are processed into a task management system. One thing is for sure: everyone with an iOS device probably uses email. Outlook was chosen for its focused inbox option, snooze options, a built-in calendar, and a wide range of support for various email systems.
Read the entire review over at The Sweet Setup. You can download Outlook for free on the App Store.