Tutanota is the only email service that automatically does this. Instead of using an implementation of PGP itself, Tutanota uses standard algorithms also being used by PGP (AES 128 / RSA 2048) for encrypting not just emails, but also other information that ProtonMail does not encrypt such as the entire address book and calendar metadata like calendar notifications. Additionally, the encryption protocols used in Tutanota enable us to easily upgrade to new algorithms and add support for Prefect Forward Secrecy. Tutanota encrypts not just bodies and attachments of emails, but also the subject line, which can contain very sensitive information. ProtonMail uses PGP encryption, which lacks important requirements that Tutanota is able to fix. In addition, there are quite important differences in the encryption methods used. One major differentiation here is that in Tutanota external recipients can access the entire email thread via the shared password while recipients of encrypted messages from Proton Mail are limited to just seeing one message. Both Proton Mail and Tutanota offer end-to-end encryption for all emails, and both enable users to use a password for encrypting emails sent to recipients that don’t have an address with an encrypted email provider.

Proton mail