Jorun, As far as I can tell the "notifications" set-up is all in order.
I asked Fred the technical administrator to look into it too. He says that some people's email provider may be rejecting / treating the notifications as spam. This is a real problem with some providers especially Hotmail and other Microsoft-hosted emails; AOL is another. There is nothing Fred can do about this. If that is happening the notifications might not even be reaching people's spam boxes.
Even so, it would be a help if anyone who has had notifications go missing could let me know, ideally saying exactly what threads/postings were involved.