What fruitoftheloom is trying to tell you is that you have a very high (beta) version of Thunderbird, and more to the point: not the version that comes standard with Raspbian. And that's where the problem is, that version is not working with Enigmal from the Raspian repository.
The Enigmail website says you should install either the official Thunderbird version from the Mozilla website with the official Enigmail version from their website, or stick to the versions in your distribution, which is probably the easiest way.
So my suggestion is that you remove Thunderbird from your Pi (you somehow installed it yourself, so use the proper deinstallation procdure) and install Thunderbird and Enigmail from the standard tools you have:
Code: Select all
sudo apt-get update
sudo apt-get install thunderbird enigmail
I am trying to install Enigmail myself now to test it. Generating the key takes a while, but it seems to be going well.