If your Mac is connected to the Internet but suddenly starts asking for your password, you should generally try again later, and if necessary work with your email provider to resolve. In the right pane, enter a new password in the Password box.

In the left pane, click the account in which you want to change the password. Type your current pst password (or leave it blank if you your pst file is not password protected), then type a new password and confirm it. Double-click on the Outlook.pst file that you want to change the password on.