I don't use the feature, but if you schroll down to the bottom of the page you are viewing now, at the bottom right you will see and ACTIONS box where you can "Toggle e-mail notification".

I believe you will receive an email any time someone replies to that thread.  Please be aware that if you "mark" a large number of very active threads you may recieve so many emails that your email server may consider NewAgTalk as a spamer and block those emails.