I've created a broader solution with pattern matching:
[nodebb-plugin-email-whitelist] Email domain filter plugin 😉
CAPTCHA on registration
To secure the forum from spambots a CAPTCHA would be handy. On our site we use playthru, a free non-annoying CAPTCHA.
What's the URL of your site?
Yep, it looks good. It will definitely cut down on bot registrations, but will not stop human spammers. IP bans and post deletions will take care of those.