I made it to that only members can view links
But how can i make it so that they can post them, too?
A forumer can't post links on my forum

Has the user joined your forum within a week?

General>Forum>Security
Unauthorize members with less than a week registration to post external links and emails : No
Save.

Its not advisable to change it to No, as it gives spammers the freedom to post links as well.

Solved