Communication security is an increasingly important subject. K-9 Mail aims to provide intuitive e-mail security in many forms, both in terms of supporting secure login to your e-mail server and in the security of the e-mail itself.

To this end, K-9 Mail supports a variety of mail server authentication methods and has had longstanding support for OpenPGP and future plans to support S/MIME.

Server Authentication

We currently support the following secure authentication methods

We support both the STARTTLS and running over TLS. We review our TLS protocols and ciphers in response to recent attacks.

Encryption & Signing Emails

K-9 currently supports PGP/MIME encrypted e-mail through an open API that any application can implement in order to encrypt and decrypt e-mail. We have worked on this API along with the developers of OpenKeychain, a security-audited application that supports PGP.

For more information on using PGP/MIME in K-9 see our documentation on PGP/MIME.

The other common e-mail encryption and signing implementation is S/MIME. K-9 currently does not directly integrate with any S/MIME providers. Some apps may provide S/MIME functionality but they are neither maintained nor do they directly integrate with K-9. For information on S/MIME see our documentation