Hej, I did a search on this if there was another topic about it, well I didnt find it, so I am sorry if there is out there and I am just really blind!
 
But I would like to have a Group, a new group that is 0 in posting and can see the forums but Nothin gin it except for one forum which is the introducing forum.
So when they have said hello basically they can post and see the topics in other forums.
 
Now I made a group that is 0 in post, but I can change/edit the permission in the rights of the forum.
 
Any help would be much grateful. 

From what i understand of your problem. You can do the following.

Create two groups.
Group 1: 0 Posts to subscribe.
Group 2: 1 Posts to Subscribe.

This way set the permissions for Group1, as being able to see just one forum. Where they can reply or post a topic once based on your preference.

For group 2, set the permissions to view all the other forums.

Hope that answers your query.

Thank you = )

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