Enigmail! It's great for remaining secure.
When it works, anyways. I seem to have a bit of an issue with Enigmail in which I can click on an encrypted email, but the email simply shows a blank page and no error message is thrown. I can't tell what is broken, and no FAQs are really being helpful, either. I've tried a reinstall of gpg and gpg2, but that doesn't help either.
Ubuntu v16.04, Thunderbird v38.8.0, Enigmail v1.9.3
gpg-agent. Is GnuPG working fine if used from the command line?
gpg-agentare sometimes really difficult to track down, and involve heavy usage of the command line and manually starting
gpg-agentwith extended logging. Glad to hear you were able to resolve the issue, anyway.