If you get this error message popping up whenever you check your emails using a program such as Windows Mail, the chances are that you’ve got ‘Secure Password Authentication’ set in your email settings and secure password authentication is not actually supported. If you are using Windows Mail, find you current email account settings by clicking on the ‘Tools’ and then ‘Accounts’ menu option. To resolve the problem, open your account email properties and untick the ‘Secure Password Authentication’ box. Save your changes and away you go.
Once unticked, that irritating popup error window should now have disappeared when you next go to check your emails.