So it looks like by default, there still isn't an e-mail sent unless the user goes to their "Settings" and changes
"When a new reply is posted in a topic you are watching" to Notification & E-mail.

Is there a way to default that to "Notification & E-mail" for users?

Oh, awesome! Found it, and will give it a test. Thanks!

Got a nodeBB instance up and running. We're planning to use it for our community and as support. Based on testing it out, one concern I have, though, is that users who ask a troubleshooting question won't be notified unless they check the specific topic in the forum. I installed the nobebb-plugin-category-notifications plugin so that you at least get notified if you're watching a topic, and I've configured it so that it sends an e-mail as well.

Is there a plugin or a way to configure things so that when a someone responds to a topic you started, you get an e-mail notification? I want to make sure people don't necessarily need to be on the forum at the exact topic to see that someone has responded.

Or (given the way I have things set up so far), automatically "watch" a topic that you start?

Or am I missing something completely obvious?