Email Security

Is there a way of encrypting email from lan connected PC’s so that the email I may compose is encrypted in transit and also while it is residing on the exchange server waiting to be transmitted and does it stay encrypted when the specified user receives the email if they don’t have the message open does it remain encrypted ? I would like to keep the email encrypted no matter where they are stored, wether it be on the Exchange server or if they are copied or moved to a personal directory on a local PC. Is this possible ?? If so what program would you recommend for Outlook ?

Thanks.