The site could be temporarily unavailable or too busy. Try again in a few moments.
   If you are unable to load any pages, check your computer’s network connection.
   If your computer or network is protected by a firewall or proxy, make sure that Thunderbird is permitted to access the web.

TB was working fine, but now I can no longer send email. I get a popup window with this: Unable to connect An error occurred during a connection to localhost. The site could be temporarily unavailable or too busy. Try again in a few moments. If you are unable to load any pages, check your computer’s network connection. If your computer or network is protected by a firewall or proxy, make sure that Thunderbird is permitted to access the web. The service (Comcast) is up & working. I've double-checked the password. I've tried disabling my firewall. How do I figure out what is now causing the problem?