Entering Your Username
If Outlook asks for your password, change the username from etsu\username to your e-mail address (firstname.lastname@example.org): Do not include the word "mail".
Previous Method to enter username and domain:
CORRECT method to enter username:
If Outlook saves your password, from the Tools menu select Accounts and change your username from etsu\username to email@example.com as shown:
Allowing Automatic Discovery
Outlook will ask permission to autodetect your new account settings, click Allow. It will probably do this several times:
Lastly, check the box "Always use my response for this server" - Allow.