I have a total of three email addresses. Two of them are gmail. I was able to get both of them into Thunderbird. However, when I try to add my att email address, it does not accept it. (I know I am entering the correct password, because the password works when I get into my att email address when I am on the Internet.) After going through the configuration, I press "done" and then after a long time of checking the password, it says it is unable to log in at server.  ??