Please. Captcha by default. Email domain filters. Auto-block federation from servers that don't respect. By default. Urgent.
And yes, to refute some comments, this publication is being upvoted by bots. A single computer was needed, not "thousands of dollars" spent.
Look up the origins of IRC's EFNet, which was created specifically to exclude a server that allowed too-easy federation and thus became an abuse magnet.
Now that’s a name I’ve not heard in a long time… a long time
that was my home network for many years