In GnuPG, if you get an error saying “There is no assurance this key belongs to the named user” when trying to encrypt, you need to sign the public key.
You can sign the key by typing “
gpg --sign-key user-id” at the command prompt.
Footnote: I came across this whilst migrating our e-commerce system to a new server. The system uses GnuPG to encrypt the order/credit card information and then emails it to our sales team. I’m making sure I document the process fully, so that I don’t have to spend so much time figuring this stuff out again! 🙂