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.
As someone with his own email domain, screw you for even thinking about suggesting domain filters.
Blacklist domain filters are fine, it's whitelist domain filters that get small personal domains.