Although I did not ask for PGP when MACBuntu was installed, it offered it as part of the install process. I stupidly said yes and now cannot send mail via Thunderbird. I have tried to cancel or change to no PGP, but the software isn't doing that.
Macbuntu & PGP !? What do you mean PGP, Pretty Good Privacy?
It is not possible. Only plug for Thunderbird is this theme https://addons.mozilla.org/en-US/thunderbird/addon/6763/ which is not automatically installed, only recommended.