Usually when problems occur post update the fault lies in the anti virus / internet security suite. So 1. check your anti virus firewall to ensure Thunderbird with it's new version number is an allowed program to access the internet without restrictions. 2. Disable the mail scanning part of any anti virus product and reboot. Either of those things help?

The antivirus firewall does not specify a version number for the software so that did not help. I am hesitant to disable mail scanning which would seem to create a new problem.

''TMT001 [[#answer-1043294|said]]'' <blockquote> The antivirus firewall does not specify a version number for the software so that did not help. I am hesitant to disable mail scanning which would seem to create a new problem. </blockquote> Interested in finding the cause? Then disable the mail scanner and see if you still have an issue. The recommended path is <blockquote> .To diagnose problems with Thunderbird, try one of the following: *Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender. *Restart the operating system in '''[http://en.wikipedia.org/wiki/Safe_mode 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: [https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode Windows 10], [http://windows.microsoft.com/en-us/windows-8/windows-startup-settings-safe-mode Windows 8], [http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-7 Windows 7], [http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-vista Windows Vista], [http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/boot_failsafe.mspx?mfr=true" Windows XP], [http://support.apple.com/kb/ht1564 OSX] ; If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.</blockquote>