spam protection in PMS plugin

Today, a new user registered and within minutes sent private messages to a number of people.
Not sure how this person selected users, it is sort of a wild mixture.
Approx. 30 people were spammed with messages regarding a business idea, then it suddenly stopped.

I wish I could configure something like a flooding mechanism, or at least the ability to add addittional measures for new users, for example captcha, until they have been there for a week or sent theit first 10 or so messages.
Or maybe an alert that stops messages from users who flood the system until I have had a chance to review what is going on.

We are using joomla!4.3.3 and CB Version 2.8.0+build.2023.07.26.22.45.22.f8ec2a4c2

CB AntiSpam can provide captcha for the PMS. Custom access checks can be implemented using CB Auto Actions, which could be as simple as on their next login after a week of being registered give them XYZ usergroup that is included in a viewaccesslevel that is used as the create access for private messages or go as far as to act on the PMS triggers and implement completely custom access checks.