If you assume your office email is for your use and no one has the right to look at it. You are wrong. Your boss can look at your email any time they want. You should not give out or use your office email for anything other than business related correspondences.
You should have a separate email for family and friends. I would suggest getting a free Yahoo or Hotmail account. Here again, this email should be checked away from the office (or maybe during your lunch hour, if the boss allows). Studies show that a tremendous amount of productivity is being lost to non-business related email.
All office email should relate to your job and nothing more. Do not use it to sign up for news, weather, or sports feeds unless they are business related. Your employer has the right to walk into your office at any time and look at your email or, for that matter, anything on your computer.