Yes it's right, you're boss have the right to read your email especially if it is work related, but if you would like to put some protection, you can do it with your Microsoft Outlook by putting a password on your personal folder.
You can select your personal by:
1. Clicking View on your menu bar, then Folder List and select your personal folder on the list. It may look like this "Outlook Today - [Personal Folder]". Or,
2. Click File on your menu bar, then Folder, then Properties for "Outlook Today - [Personal Folder]".
Once the Dialog box is show, click the Advanced button and a new dialog box will be displayed. From there you can see another button - "Change password button".
The password you can use is any password different from your login password. Just don't forget it. :)