Since I’ve started using Gajim I’ve been trying to get it working using the GPG Agent rather than the built-in GPG option. The practical benefit is that I’m no longer required to insert my passphrase each time I open up my laptop, as the passphrase is part of my keychain, just like I have enabled from my Evolution email client. It took me quite a while to get it working, and looking by the number of reported tickets others had difficulties as well. I finally got it working by ultimately trusting the receivers key. In order to keep others from having similar issues, I’ve filed a ticket on the trust level and a ticket on the error.