ProtonMail has zero access encryption at rest for your emails, address book contacts, and calendars. This means the messages and other data stored in your account are only readable by you.
ProtonMail has integrated OpenPGP encryption in their webmail. Emails to other ProtonMail users are encrypted automatically, and encryption to non-ProtonMail users with a OpenPGP key can be enabled easily in your account settings. They also allow you to encrypt messages to non-ProtonMail users without the need for them to sign up for a ProtonMail account or use software like OpenPGP.
+ProtonMail has integrated OpenPGP encryption in their webmail. Emails to other ProtonMail users are encrypted automatically, and encryption to non-ProtonMail users with an OpenPGP key can be enabled easily in your account settings. They also allow you to encrypt messages to non-ProtonMail users without the need for them to sign up for a ProtonMail account or use software like OpenPGP.
ProtonMail also supports the discovery of public keys via HTTP from their Web Key Directory (WKD). This allows users outside of ProtonMail to find the OpenPGP keys of ProtonMail users easily, for cross-provider E2EE.