Exclude certain forum categories from notification

Hi all

I have been using notifications on my site for almost a year now and it works like a charm! thanks for the great work!
Now I have encountered a problem:
I would like to create a "internal forum" where only special users have access. The problem is, that whenever a post is done there, then everybody gets a notification. How can I change it so that only the group with the role "special users" get a notification when a post in "internal forum" is done?

thanks for your help!