If you have a password protected Outlook Data File (.pst) and didn’t select the Save this password in your password list check box, when you open the file, you are prompted for the password.
If the password that you type inside the Password box is incorrect, an error message appears.
Passwords are case-sensitive. Accidentally turning on CAPS LOCK is a common reason why a password attempt fails.
Important: If you forget your password, Microsoft can’t recover it.