private emails in Outlook 2010

Hi, I have personal assistants who have full access (including send) to directors' mail boxes in Outlook 2010. Another user would like to send an email to a director but does not want the pa to be able to read/view the email.

Is there a way in Outlook 2010 to make emails private or encrypted so that pas would not be able to read them despite having full access?I only want the intended recipient to be able to read them. Thanks