moz. thunderbird ...wont sign in

Instructions for setting up a centurylink.net email account are provided here: https://www.centurylink.com/home/help/internet/email/how-to-set-up-your-email-server-settings-to-go-through-pop-and-smtp.html If using IMAP, you may find them clearer here: https://www.postbox-inc.com/setup/email-settings/access-centurylink-net-via-imap-smtp The error message you're getting, if quoted correctly, makes me think you didn't type the full name of the mail server, so make sure you're setting up the account correctly according to those settings. If the problem persists, post a screenshot showing the settings you're trying to use.