Hey Caroline, This should be possible, I believe the article you linked is incomplete and we should be able to support # of posts in x time period regardless of whether they have the same subject. Please open a support ticket as suggested and they should be able to help out. I have also reached out to our documentation team to clarify the article you linked. Thank you and hope this helps, Yuri ... View more

Apologies, I quoted the wrong setting above. This one should do what you want: Require verification for  users to post messages:  presents  challenge  when users try to post new Forum messages.  This option also requires that the  Post  messages without verification  permission be set to  Deny  for the desired roles in your community.   Note that you will have to set the permissions accordingly for users you want to have captcha show up. Hope this helps, Yuri ... View more