ProtonMail is an encrypted email service, with native applications available for Android and iOS. While the service has been working on new features, its development team has also been releasing the source code for various software components. Now the Android app for ProtonMail is open-source, allowing anyone to look through the code and review its security.

"Starting today, every app you use to access your ProtonMail inbox is open source and has passed an independent security audit," the company said in a blog post. "One of our guiding principles is transparency. You deserve to know who we are, how our products can and cannot protect you, and how we keep your data private. We believe this level of transparency is the only way to earn the trust of our community."

The Android app was the last ProtonMail client to be open-sourced, following the web app, iOS app, and desktop bridge. The code is now available on GitHub, and it has passed an independent security audit from SEC Consult.