To disable “Do Not Disturb”.
1. Tap the Nav icon at the left of your navigation bar to open the Navigation Drawer.
2. Tap the Gear icon at the bottom of the Navigation Drawer to bring up Settings.
3. Tap Mail.
4. Tap Notifications at the top of the screen.
5. Tap Smart Notifications.
6. Tap Do Not Disturb.
7. Tap the Do Not Disturb slider to disable the feature.