Thunderbird update - version 78 or newer requires additional configuration – DotCIO - IT Services and Support Center

Symptoms

Thunderbird version 78 or newer causes issues with email sending and receiving.

Additional Thunderbird configuration step for version 78 or newer:

Go to Options -> General tab on left -> scroll all the way to to the bottom to click on Config Editor
Click on I accept the risk
In the search, put in security.tls.version.min -> press Enter -> change value to 1

Thunderbird update.

https://itssc.rpi.edu/hc/en-us/articles/360009463771-Thunderbird-Configuration