This function used to be addressed in forums via the Forum Administration - flood interval setting.
As a means to block spam for a forum, you can configure the number of posts the system will accept from a particular IP address.
To enable the rule:
- Navigate to Control Panel Dashboard > System Administration > Site Administration > Content/Site Security > Manage Spam Blocker > Rules.
- Select the check box for Forum IP address frequency (used to determine if a given IP address attempts to make repeated posts).
- Click Configure.
- In the dialog, enter the following information:
- Threshold - Maximum number of posts that can be created from the same IP address within the specified duration.
- Points - Number of points to assign to each post beyond the threshold above.
- Duration - Number of seconds to search for posts from a similar IP address.
- Excluded IP addresses - Addresses, for example for your router or local IP, to protect from being scanned.

- Click Save. The dialog box closes.
- Click Save in the Rules tab.