After struggling to get the whole PGP thing to work, I uninstalled everything and re-installed it all again.
This time, when I try to encrypt an email, in the select recipients window I have two that I've added (apart from my own details). Both of the two have the text greyed out, are "untrusted" and therefore the only checkbox I could possibly tick is my own keypair.
One of the recipients is the test account adele-de at grupp.de, the second is a friend who sent me his public key and I imported it into the key management list.
What I am I doing wrong this time?