Microsoft has released a new update for Outlook for iOS app. This new update enables you to focus more on the email you are reading by allowing you to collapse the message list. Outlook team has also tweaked the experience by reducing the margins and showing more of the content. When viewing mail full screen, you can now swipe right/left to move to next/previous mail.
This full screen feature is available on iPad & iPhone when in landscape mode. Download the updated app from App Store.