Follow this steps :-
-Go to the File tab.
-Select Info.
-Select Account Settings > Account Settings.
-In the Account Settings dialog box, select the email address for which you want Outlook to remember the password, then select Change.
-In the Exchange Account Settings dialog box, select More Settings.
-In the Microsoft Exchange dialog box, go to the Security tab and clear the Always prompt for logon credentials checkbox.
-Select Apply to apply the changes, then choose OK to close the window.
-In the Exchange Account Settings dialog box, select Close (X).
-In the Account Settings dialog box, select Close.
-Restart Outlook.
hope this solves your problem