This is most likely due to your firewall and/or antivirus software on your computer.

This security software recognized the previous version of Thunderbird on your computer and was set to allow it to communicate with the Internet. After the update, the security software saw that Thunderbird was not the same, and decided to block it from communicating with the Internet.

So the probable solution is to tell your firewall and antivirus software that the current version of Thunderbird is allowed.

My guess is that you are using Norton. It is the main culprit with problems like this.

Thanks for your reply. I do use Norton. Under the Firewall settings I can see that Thunderbird.exe is set as Allowed.

I found a specific error message in Thunderbird, using Tools/Error Console. Here it is: Timestamp: 1/30/2017 8:25:38 AM Error: An error occurred executing the cmd_getNewMessages command: [Exception... "Component returned failure code: 0x8055000a [nsIMsgIncomingServer.getNewMessages]" nsresult: "0x8055000a (<unknown>)" location: "JS frame :: chrome://messenger/content/mailWindowOverlay.js :: GetNewMsgs :: line 2712" data: no] Source File: chrome://global/content/globalOverlay.js Line: 103

Restart the operating system (Windows or OSX), in Safe Mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP, OSX.

Then see if Thunderbird works better. If it does, then another program or process is interfering with Thunderbird when Windows is running normally. This will likely be Norton.

Then report back.

Thanks for your quick reply. Bingo! When I start in safe mode, Thunderbird works as normal -- gets all my messages.

I restarted the computer in the normal way and Thunderbird was still working as it should. So it looks like that two-step restart process got things back to normal.

Thanks for your help.

Thanks for your quick reply. Bingo! When I start in safe mode, Thunderbird works as normal -- gets all my messages. I restarted the computer in the normal way and Thunderbird was still working as it should. So it looks like that two-step restart process got things back to normal. Thanks for your help.

Well, it shouldn't work that way, but whatever. You have things working again.

I figure that Norton is going to cause you problems with e-mail again in the future, so disable it's e-mail scanning anyway.

It is recommended that e-mail scanning be disabled in antivirus programs, because antivirus programs already automatically scan everything when it is accessed. So e-mail scanning is an unnecessary duplication, and that e-mail scanning itself can cause problems.