I find that if you get a little red alert saying someone has replied and you click the alert but don't visit the actual thread then the emails will stop coming through but you will still get the little alert on your profile.
The less you visit the thread the less emails get sent.
One click on the notification bell icon should give you a drop down list - click on a thread. If there was more than one item in the drop down, just click the bell and the list will reappear. Double click on the bell and you'll get an all-time listing starting from the newest. Also, once you have looked at the drop down list, the red number flag is cleared. It will reappear (with the number 1) as soon as an alert is subsequently set.
A notification to one thread maybe should say, 'there may be more after this'. Say there were three posts to a thread you are watching. I think you will only get an email when the first was posted. No more email will come to you until you visit the thread. When you do, you will get an email when there is a new post since your last visit - in our example, not until the 4th post (which didn't happen until after you visited the thread).
gawd, I'm getting to be such a tedious old man.