I was trying out the latest Thunderbird release today and having issues getting my OpenPGP key working via my Yubikey. I had already enable the use of external GnuPG and set the path appropriately to the gnupg binary. After delving into the Thunderbird developer console I discovered an error “request to use external GnuPG key, but GPGME isn’t working”.
Turns out that GPGMe is not installed by default when installing GnuPG via Homebrew on MacOS. After installing the separate GPGMe package I was able to use my OpenPGP key stored on my Yubikey without issue, or so I thought. I was able to send an encrypted email no problem but receiving one didn’t work. Everything looked good, but Thunderbird couldn’t find the associated private key. Until I unplugged and re-inserted the Yubikey. Then everything was happy again… until next time I suspect.