The setting just ban member after registration:
public function profileSync()
{
[...]
foreach ( \IPS\Db::i()->select( 'ban_content', 'core_banfilters', array( "ban_type=?", 'email' ) ) as $bannedEmail )
{
if ( preg_match( '/^' . str_replace( '\*', '.*', preg_quote( $bannedEmail, '/' ) ) . '$/i', $this->value ) )
{
throw new \DomainException( 'form_email_banned' );
}
}