This is something that I have been reporting for a lot of years and a lot of versions.
I have around 40-50 spambots registering in my website every day. And while I am searching for a solution on how to Install Recaptcha , I see that even the domain block does not work!
For example I have blocked this domain in Registration and they keep registering!
Also why I can't use wildcards like *edu.pl ? Because I have a lot of emails from there with variations.