It's not really been possible since the Anyone cc and Registered groups were merged a few years ago. However, try one of these approaches.
Create a 'New User" area and invite new users to post there. Remove the Reply permission for all users to that area. Add those posting acceptable introductions to the Member group. You must be in the Member group to post in any other area. This approach limits spam to one area but does allow subscribers to the top level to see the spam.
Alternatively, post instructions on how to apply to be a member in the New User area, rather than putting them in the area description and then turn off posting rights in that area for everyone. Your instructions tell users to click on you username/avatar and select the option to email you. If their application is acceptable reply saying you've added them to the Member group. Only members can post elsewhere in your forum.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.