You encrypt your message with the recipients email address as key. You also can define how long the message will be readable by specifying an expiration period. If you have something really secret, you may enter an extra PIN or pass phrase. You must inform the recipient about this extra PIN, because otherwise s/he cannot read it. Then send your message. The recipient will get the encrypted message in the Inbox of the mail client. In order to decrypt it, a personal key must be requested here. The personal key is protected by a customer chosen Pin or pass phrase and is delivered by email to the email address specified in the key. Then the gets activated and the recipient can read your mail. So easy.