Thanks!

~$ torsocks curl -s https://check.torproject.org/ | grep Congratulations.
 Congratulations. This browser is configured to use Tor.
 Congratulations. This browser is configured to use Tor.

Still no go in Thunderbird with setting up the proxy. I'll dig into it more, because I think that's the ticket. The TorBirdy plugin is outdated and has been for a while, which is what seems to be used previously. I may boot up in Tails or something similar to see if the issue persists.