FortMail

FortMail – free, reliable, protected e-mail client aimed to receive, compose, send and store ordinary or encrypted e-mail messages of one or several users, or several accounts of one user. It uses SMTP and IMAP protocols.

E-mail client has simple, user-friendly interface.
This is free version for private use. No advertisements, in-app purchases, paid updates. Totally free.

Encrypted messages exchange is possible only among users who have FortMail installed. FortMail uses end-to-end encryption. Keys necessary for decryption are stored on user’s devices. FortMail uses RSA algorithms (2048-bit, OAEP pading), AES-128 CBC (random IV) and SHA-512. Public keys exchange is performed through FortMail server during message composition. Key generation (AES and RSA couple) is accomplished on the basis of unique device and user data. Message encryption is performed on AES key. AES key is encrypted with recipient RSA public key and is attached to the message.

After uninstalling and reinstalling of the application, the keys are regenerated and decryption of the old messages will be not available, which confirms that the key is unique and will not give a chance to collect your encrypted information. In case if you have more than one device attached to FortMail account you will have possibility to view old messages on them.

FortMail CCA crypto container is safe and protects message text and attachment.

Strong device-to-device encryption among FortMail users.