under 'Mail Sending Method'
try checking [Authorize by Checking Email] and fill out the line below it.
SMTP sending - This option is highly recommended. Sometimes, a setting of "localhost" as your host, with no additional authorization, works best. If a remote test does not succeed, you may need to enable AUTH to validate your username and password. Furthermore, your host may or may, or may not, use "POP checking" for authorization. This is where the server allows people who have checked mail recently to send email for a certain amount of time. To be sure, check your host's mail sending FAQ. If your server calls for you to check email every 20 minutes, for example, enter "19" in the "Every X mins" option for the feature