You can't at the moment. It's on my todo list in the short term... as in before the new year.

Coolness .. thanks fer the response.

When is it going to be available?

If you mean you want to get emails when someone adds a response to a forum topic you have also added a response to, then this has already been added as a feature: when you reply, make sure the box next to "Email me about all replies to this article." (underneath "Formatting info") is ticked.

If you want emails from forum topics you start, then make sure the "Email me about replies to this node." box is ticked.

I this it is Option when you are posting comment