How would it encrypt email on a rogue machine, securely? If the machine is rogue and has all key presses and has the plaintext how can it be secure then? Sure it is encrypted but it is already compromised.
Oh, sure, the current email is compromised, but not the key (since the encryption/decryption is performed by the card itself). The advantage is that you can use a public machine to check a non-important email without giving them the keys to all others or letting them email faking your identity.
