Article 16

Replying to andrea_r:

As an extra, anyway you could make the same in the DISallowed email field? So super admins can block all *.info or *.ru domains from signing up (for example).

is_email_address_unsafe() seems to support regular expressions:

if (
	strstr( $email_domain, $banned_domain ) ||
	(
		strstr( $banned_domain, '/' ) &&
		preg_match( $banned_domain, $email_domain )
	)
)
return true;

According to comments on #14695, it's possible to use something like /.*\.info/.