There are two ways to enable auto-email responses.
#1 Check the box "email notification" when you start a new thread or post a reply.
#2 Click the "edit" icon on any post you have already made on a given topic, check the "email notification" box and then re-submit your original post.
Similarly, if you elect to no longer receive email notification on a given thread, you may simply go back and edit your post and uncheck the box to stop any further email notifications on that topic.
This should be a very handy feature for anyone following a specific topic they are participating in, as well as for anyone who forgot to check the box at the start of a new thread. Enjoy! 