How secure is Proton Mail?

The security of our users is one of our top priorities. Here's how we make Proton Mail secure:

• End-to-end encryption: Messages between Proton Mail users are transmitted and stored on our secure servers in an encrypted format. Because your data is encrypted at all steps, the risk of message interception is largely eliminated.
• Zero access to your data: Only you have the key to decrypt your messages and files stored on our secure servers. Your data isn't accessible to anyone else — not even us. As we don't have the key to access your data, we can't hand it over to third parties.
• Password-protected Emails: Messages between Proton Mail users are end-to-end encrypted automatically. But you can also send end-to-end encrypted messages to people on other email providers using Password-protected Emails or standard PGP encryption.
• Open source: All our apps are open source and independently audited, so anyone can check our code.
• Strong physical security: We've invested heavily in owning and controlling our own server hardware. Our data centers are located at highly secure sites that require biometric access.