How to Set a Password on Your Outlook Data File
 

If you’re concerned about protecting your email in Outlook from prying eyes, especially if you share a computer with others, you can protect the email in each Outlook account, as well as the calendar items, tasks, etc. by setting a password on each Outlook data (.pst) file.

http://www.howtogeek.com/244260/how-...ook-data-file/