For whatever reason, Mozilla who develop Thunderbird have stopped accepting TLS1.0/1.1 security protocols. This may cause an issue when using GENZone and GENX, but not Dakota. The message received may be like this:

"Sending of the message failed.
Peer using unsupported version of security protocol.
The configuration related to mail.genzone.net must be corrected."

To resolve this you will need to make changes to your thunderbird configuration. To do this follow:

Windows : Thunderbird, choose Tools –> Options –> Advanced –> General and press the Config Editor... button.
Mac/Linux : Thunderbird, choose Preferences –> Advanced –> General and Config Editor.

Accept any warning that comes up and you should have a list of settings with a search box at the top. In the search box type (or copy/paste)

security.tls.version.min

And you should see a screen that looks like this:



Double click the setting and make sure its set to 1
Then close the settings box, close options and quit Thunderbird.
After its quit, reload it and it should work as expected.