Question about banning mail domains (if I understand correctly), answers about banning countries from registration.
You may just a ban email domain via ACP and default feature: /admin.php?banning/emails
FWIW, I use both methods: there are certain countries that I block completely using Cloudflare - they can't even view my site.
There are other countries that can view the site but can't register at all (using my addon). I also have it set up so that there are some countries that can automatically register - and then registrations from all other countries get sent to moderation for approval.