Account can't log in to imap server

A Thunderbird email account which worked for years suddenly started sending the error message "Login to server imap.comcast.net with username rbhollimon@comcast.net failed"; no new email messages can be accessed by this account . The username and password have been carefully checked and appear to be correct. Another email account still works. No settings for the account were changed by us. A mobile phone has for years had access to this email account and messages could be read on the phone. The ability to read messages on the phone disappeared and attempts were made on the phone to restore the ability to read them. The login errors on Thunderbird began immediately after this onphone attempt. So far all attempts to fix this problem have failed. We need to restore the ability of this account to acquire new messages in order to preserve this email address. Any help with this problem will be greatly appreciated.