Your Android device includes a security option in system settings to “hide sensitive notification content” (see below). If you have this setting enabled, your apps, including ProtonMail, will not display the email address and subject in new mail notifications.
Extended Notifications in the ProtonMail app allows you to override this system setting, letting you see the sender and email subject in ProtonMail notifications while maintaining the setting for all other notifications on your device.
Follow these steps if you want to hide sensitive notification content on your Android device:
1) Navigate to your Android settings and select Security.
2) Change the Screen Lock to Pattern, Pin, or Password.
3) Select “Hide sensitive notification content”.