Allows users to receive emails for replies to their comments (or optionally for all comments on a node). Can be toggled by content type (although not by comment type, if you have more than one comment entity). In permissions, you can also control which roles can subscribe. Can also set it so the author of a node also automatically gets emailed for every comment.
I'm using three patches:
- User without Subscribe to comment notifications sees setting in profile (authored by me)
- False positive notifications with multiple comment types (authored by me)
- Notifications not sent when user chooses 'Replies to my comment'
I also have a site which uses two comment types; I wrote a patch to turn off the notification checkbox for one of them.