Make sure Thunderbird isn't blocked by a personal firewall.

Don't think I have a firewall problem. Don't know how to check.

Maybe I should uninstall Thunderbird and re-install it? Comments>

Larry K

Waste of time. Figure out what firewall you have and make sure Thunderbird is Allowed. Firewall is usually part of your antivirus.

Thought I sent a reply, but don't see it.

email is fine on two other computers (Windows 7) that did not have an upgrade of Thunderbird. Windows 8.1 computer did have upgrade and now has the problem,

ISP (cox.net) does not support Mozilla. Bummer!

Firewalls all seem fine for Thunderbird. Still can't connect.

Now what?

Larry Kunkel

I ran a "severe" virus check with Norton 360. Now, all is well with Thunderbird and also Firefox--which also was affected when I did an update.

I had uninstalled Thunderbird, but it came back just fine when I re-installed it. Also, I now have Firefox okay, too. Happiness is running virus software to fix problems!