Another terrific free service for business, home, and the paraniod; is ziplip. Ziplip offers 2.5 mb of storage and the ability to send regular mail or very secure mail. Ziplip simply encrypts and saves the message in a secure environment and sends an email asking for a password. Your contact is then able to access the email upon replying with the password. Of course, the password must be pre-determined by both parties but there is a password hint included. So, if you are 007, exchanging insider info about the stock market, sending info on that new hydrogen engine you just invented, or simply sending love letters to your mistress, this service may be for you.
https://www.ziplip.com/ps/app/services/home.jsp