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.
That's like saying "My corporation doesn't need anti-virus! we have smart users!"
Defense in depth is the only philosophy that makes sense in this case imo.