In January, we released Outlook for iOS and a preview of Outlook for Android. At the time, the iOS version of Outlook was ahead of the Android version in terms of features and performance. We set a high bar for where we wanted Outlook for Android to be before we removed the preview label. Since our preview release we’ve updated Outlook for Android 17 times—that’s more than one update per week—to meet this bar. A big part of that work has been improving the performance and stability of the app along with work on localization, accessibility and other fit and finish pieces. The other part of this work was about delivering features to add new value, match the iOS version and respond to your feedback.
Read more at source: http://blogs.office.com/2015/04/22/outlook-for-android-comes-out-of-preview/