This is a simple ContentBox module that will E-mail blog commenters when another approved comment is posted on the same blog entry.
The E-mails will go out when the comment is saved IF it is approved.
Otherwise, they will go out any time the comment's status is changed to approved-- even if done in a bulk update.
There is no need for commenters on your blog to subscribe. The is also no way for them to unsubscribe-- if someone doesn't want to get further E-mails, then just remove their E-mail address from their comment.
This module is just a stop gap until full notification support is introduced in ContentBox 2.0.
Much of this code was adapted from code Andrew Scott (http://andyscott.id.au/) shared on the ContentBox List.
Just install and activate the module in the ContentBox admin and that's it.