When you write a new message, there is now a checkbox option that reads:
(X) Email me replies to this message

A similar checkbox now appears on the "leave a comment" box:
(X) Receive this thread by email

If you check this option, you'll receive email copies of replies (aka comments) to your message, and only your message. You'll also receive a link in each email to optionally stop the emails (unsubscribe)

This feature strikes me as very handy when you don't want to receive all the email from a forum, but do want to hear back about your particular question.

Note: this option does not appear if you are set to receive all emails from the forum.

You can also choose to receive/stop email for a thread from the pulldown menu when ready any message thread.