@lnxw48a1 I have disabled federation with #tigase.im on my server (snackr.se) because it's open-registration and lots of spammers.
(I've had to shut down open registration on my own server because of spammers registering).

I'm considering getting a captcha that can only be solved by spreading via word of mouth. (admin sets the captcha phrase, people who know the admin asks for the phrase and receive it, and can thus present it to new recruits).