Hello,
you can use the feature Filter user registration by email : https://www.akeeba.com/documentation/admin-tools-joomla/web-application-firewall.html#waf-configure-joomla-hardening
It's meant to block (or allow) specific domains, but we can force its behavior to block all .ru domains. In the Email domains field, simply put .ru. That should do the trick and block any email address containing the .ru string.
As a downside, if [email protected] tries to register to your site, he will be blocked. I suggest you to enable this feature only for a few weeks, usually spammers will go away and start hammering another site.
Davide Tampellini
Developer and Support Staff
๐ฎ๐นItalian: native ๐ฌ๐งEnglish: good โข ๐ My time zone is Europe / Rome (UTC +1)
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!