To encrypt an email in Canary Mail, you will require the recipient's public key. As long as you have the correct key the lock symbol will turn Green (for iOS and Android devices) and Orange (for macOS devices) which indicates if an outgoing email is encrypted or not. You may verify that your sent emails have been encrypted by opening your message in another email client. You'll see an attachment in the body of your emails which are completely encrypted and unreadable. Your recipient can decrypt the email using their secret key (which corresponds to the public key used to encrypt the email).