In the mean time I fixed my problem by searching all the ASP-files were the notifaction-messages where introduced. 
In the file post_message.asp I changed the paragraph
*** Send Email Notification **
The first line was:
If blnEmail = True
My new line is:
If (blnEmail = True) and NOT ((intForumID=1) and (strMode <> "new"))
So now a notification is only send (in forum 1) when a new topic had been made. Reply's, new polls etc will not produce a notification-message.
Are my thougts correct? (I am not a real ASP-programmer, so it's possible that I'm not fully correct). 
Hopefully my small adjustment brings other people to new ideas.