Mozilla disabled TLS 1.0 and 1.1 in the latest versions of Firefox and Thunderbird. Thunderbird 78 and above.
This causes issues with anyone connecting via SSL/TLS/StartTLS to us, as Qmail uses 1.0.
It can be enabled again through the menus of Thunderbird.
- From the menu at the top right, go to Options; on Mac it may be Preferences.
- Scroll all the way to the bottom and click on Config Editor.
- Skip past the warning.
- Scroll down until you find security.tls.version.min
- Double click on it, and set the value to 1
- Then okay it.
Close Thunderbird, and open it again; this should then have resolved the issue.
The following will also instruct you on how to access the Configuration Editor:
- Thunderbird v78, Config Editor: Windows 10
- Thunderbird v78, Config Editor: Mac
- Thunderbird v78, Config Editor: Linux