You also noted this in the emails you get right:
"This topic has received a reply since your last visit. You can use the following link to view the replies made, no more notifications will be sent until you visit the topic."
phpBB (the software that runs the forum) does this so that you will not get HUNDREDS of emails about the same thing.. until you visit the thread.
so if you get a email, and ignore it.. you won't get replies until you visit the thread again..
also helps on bandwidth on the server