User name

Insert here the name of the user you have on the external mail server: this is normally the same than Account name, but it doesn't have to, and you can get from current configuration of the e-mail client as a mail user to check.
For example, if you've user myself on an external mail server, you must put myself here, while in the Account name dialog and in your email client you can input myself_filtered, any other significant name, or just myself again.