To use email on your mobile device, you'll need to ensure that you have a 4+ character or digit passcode enabled on your device. You'll also need to be sure your device is encrypted.
Apple iOS
iOS enables encryption on devices by default, so you'll only need to ensure a passcode is set. For information on how to set a passcode on your iOS device, please click here to navigate to Apple's support article.
Android
For information on how to set a passcode on your Android device, please click here to navigate to Google's support article.
For information on how to enable full-disk encryption on your Android device, please click here to navigate to Google's support article.