Proton Mail, an encrypted email service, will support 'encryption technology that cannot be broken even by quantum computers.'

Proton Mail, an open-source end-to-end encrypted email service, announced on May 5, 2026, that it now supports post-quantum cryptography to prepare for future encryption risks using quantum computers. This support is being rolled out gradually to all plans, including the free plan, and once activated, users will be able to generate and use post-quantum cryptography (PQC) compatible keys for new encrypted emails.

Proton Mail introduces post-quantum encryption | Proton
https://proton.me/blog/introducing-post-quantum-encryption

As of the time of writing, quantum computers have not yet reached the stage where they can immediately break email encryption. However, anticipating that current public-key cryptography may become insufficient in the future, standardization bodies and technology companies are already preparing for the transition. Cloudflare, for example, has set a goal of transitioning to full post-quantum security by 2029.

Cloudflare aims to achieve full post-quantum security by 2029 - GIGAZINE

Proton Mail has so far protected encrypted emails using encryption keys such as ECC ( Elliptic Curve Cryptography ) and RSA based on OpenPGP. While these methods are considered secure against current classical computers, Proton Mail states that they could be broken by techniques like Shor's algorithm if large-scale quantum computers become practical.

One of the reasons Proton is taking action now is its concern about 'steal now, decrypt later' attacks. Attackers could potentially collect and store encrypted data now, and then attempt to decrypt it in the future when the capabilities of quantum computers improve.

The newly added feature is a PQC-compatible encryption key designed to address these future risks. Once users enable this feature, they will be able to use keys designed for the post-quantum era for new encrypted emails they send and receive in the future.

However, this measure does not automatically re-encrypt past emails. According to Proton, as of the time of writing, it will not be applied retroactively to emails in existing mailboxes, and will only protect newly encrypted emails.

The generated PQC-enabled keys can be managed in the same way as traditional RSA and ECC keys. Additionally, you can generate extra PQC-enabled keys as needed, and change their status to 'deprecated' or 'crippled,' just like existing keys.

As part of this initiative, Proton is also working on supporting OpenPGP v6 , a new framework that can handle modern algorithms, including post-quantum cryptography. Furthermore, it plans to collaborate with projects such as Thunderbird to standardize quantum-secure encrypted email so that it can be used not only within Proton but also across different email services.