I've had some feedback that the auto subscription feature when posting new forum content can be somewhat annoying. I've changed the default to NO, so in future if you'd like to receive automatic updates on postings then you can turn this on, on a case by case basis. This can be done at the bottom of the page near the Submit/Preview/Cancel buttons.
You'll continue to receive email updates for previous postings where you've been receiving the emails, unless you turn it off. This can be done by going into the topic concerned and clicking the Unsubscribe button.