Request to generate email for all content changes/additions, including comments

I would like for all node comments (I currently use Drupal only for a group-blogging solution) to generate subscriber email notifications as well.

I have seen the "Receive notification of replies to this personal blog entry" checkbox for blog submissions; I need to be able to turn this on by default for all users, without them being able to know that it even exists (such that they can't complain when they realize can't shut it off). This probably won't be so hard to do on my own.

However, what may be harder for me to hack would be a capability to allow any comment to any node in the subscription (usually organized by taxonomy) to generate an email update to the subscribers.

In short, my user group lives on email, and we need email updates for everything in your blogs.

Of course, this could and probably should at least be offered as admin options for all some or all these features.

I mark this as critical because, unless the poster hand-copies an email reference to the others, comments as of right now generate no email to everyone subscribed (...I think).

-Matt