If Ban Hammer is too much for you, I understand. But you still want to smack down users from a specific domain? Otto came up with this and it works nicely.
Copy the code into your theme’s functions.php file (just make one if you don’t have one) and change the call to .ru to whatever it is you need. I’m not 100% sure what would happen if you added in multiple calls, but this is perfect for banning just ONE annoying person.
function no_russians($login, $email, $errors) {
if (strpos($email, '.ru') !== FALSE) {
$errors->add('email_banned', __('ERROR: This email address is not allowed, please choose another one.'));
}
}
add_action('register_post', 'no_russians', 10, 3);
