Thunderbird 78.4.0 fix with our mail server.
A recent update to Thunderbird removed the ability to communicate securely with mail servers using tls1.0 or tls1.1. Our server currently uses tls1.0. There were no notes or change logs mentioned in Thunderbird's update. However, there is a simple fix to restore tls1.0 ability.
1. Navigate to Tools and select Options at the bottom of the menu.
2. In the general pane, scroll all the way to the bottom and click the Config Editor button.
3. Ignore the "This might void your warranty!" notice. Does Thunderbird even have a warranty??? Click I accept the risk! to continue.
4. Then in the search field, search for security.tls.version.min. You will see the Value of this field is 3.
5. Double-click on the Value field, change the value to 1 and click OK.
6. Close out this window, close the options tab. Restart Thunderbird and your email will be working again with CalWeb!