Wordpress: Comment Approval Email Address mentions

Nate Nuzum filed a bug report which clarified the way it's supposed to work. I responded:

Ah so it appears that settings:

• "Anyone posts a comment" goes to the post author
• "A comment is held for moderation" goes to the admin So if both are checked, emails will go to both when held for moderation. Makes sense then. For clients I will probably just check the second box then.

Nabha pointed to a Settings Discussion SubPanel page in the docs, which said:

The email notification is sent to the E-mail address listed in the Administration > Settings > General SubPanel.

I responded:

The author of the post also receives an email if you have checked "anyone posts a comment". If you check both, then both might receive an email (the author and the admin address). At the time, I couldn't find the destination specified. That codex page at least at this point specifies both if you know to look there.

Neel (snilesh) asked about having WordPress email all users when a comment is added to a post in a particular category. I responded:

Oh, sorry, kinda forgot about your comment. I don't really know an automated way to do what you want. People can certainly subscribe to the RSS feed of the comments on a post though, which you could place as a link in their newsletter. There might be a plugin for doing that sort of thing, I dunno. Otherwise if they must receive emails and you are handy at writing php scripts, you might be able to attach something to wp-cron that is triggered by comments. Anyway, unless people specifically want to receive emails for every comment, the emails might get quite annoying, especially if you get lots of comments.

A couple years later, piyushranjan143 recommended a plugin, but it seems to no longer exist.