Issues with this instance: Sidekiq keeps restarting after upgrading to 3.3.0. I think that is keeping authentication emails from being sent out if required. “Regular” email works just fine. #mastoadmin
Fixed. redis-server version was too old. Upgraded. Service restored.
So, this means I should look into backing up this instance and installing on a new version of Linux. It's an Ubuntu LTS, but should be upgraded. Or, things like this will continue to become outdated and unable to upgrade without manual intervention.