Logged In: NO

The user has now three options for the notifications. One is that he receives only one notification, and then no more until he visits the site again.
Maybe the administrator should have an option for a maximum number of notifications pro user and a maximum lifetime of the notification. So after a while older articles or forum topics, where no additional comments take place or are expected, will let the notifications pass out. Is there a point to be notified for a thread of interest after two years, when there eventually should come a new comment? The lifetime is automatically extended if a notification takes place.
Notifications in PM could automatically be cleaned up when the user did not show up during some period of time.