I installed Thunderbird and followed the instructions from: https://help.ubuntu.com/community/GnuPrivacyGuardHowto to set up PGP.
First it worked, but after restarting my system the next day, I wasn't able to open encrypted mails. I added my friends the public key again, but nothing. I discovered that all added key were gone. My own key is not saved in Ubuntu's password and keys app any more. what happened? What can I do now?
If it matters, I didn't upload my public key to any servers. I am new to the Ubuntu and IT world. Grateful you for helpful answers.