This is usually caused by a problem with your Internet connection or the settings on your phone.
Please try these steps to fix your connection:
- Reboot your phone (power off, power on).
- Update the app to the latest version. Go to the Apple App Store on your iPhone. Go to the app update section and tap update all or update only the mail app.
- Turn Airplane mode on and off (Settings > Tap the switch to the right of Airplane mode On/Off).
- Make sure that data is enabled (Settings > Cellular > Tap the switch to the right of Cellular Data On/Off).
- Turn Wi-Fi back on (Settings > Wi-Fi > Tap the switch to the right of Wi-Fi On/Off).
- Try connecting to different Wi-Fi hotspots.
- Reboot your Wi-Fi Router.
- Delete and reinstall the app.
- Upgrade your iOS to the latest version available for your phone.