...The app allows users to sign in to one or multiple Proton Mail accounts, read and compose encrypted messages, schedule emails, protect emails with passwords, set expiration timers, and organize mail with labels and folders inside a smooth, intuitive iOS interface. It makes use of Apple’s networking APIs and encryption frameworks to deliver seamless management of encrypted communications while respecting platform conventions like touch navigation, Apple notifications, and background refresh. All sensitive operations — including key handling and encryption — occur locally on the user’s device, ensuring that plaintext messages and secret keys are never exposed to Proton’s servers or third parties.