It is my understanding that I need to update my Outlook 2016 AT&T email application settings to be OAuth compatible. I have the required secure mail key. AT&T’s instructions show that I should go to the Outlook 2016 Account Settings and change POP3 to IMAP then later on enter the secure email key. Outlook 2016 won’t let me make the change from POP3 to IMAP. There is no pull-down feature to select IMAP when I try to change it. How do I make that change?