E-mail domain block in Customer Service

[ThisSmart]

Good afternoon! I want to make sure that no e-mails come for example with the domain example.com in Customer Service

I do that in ContactController.php:

$domain_name_block = 'example.com';
			$domain_name_email = substr(strrchr($from, "@"), 1);
			if (!($from = trim(Tools::getValue('from'))) || !Validate::isEmail($from) || $domain_name_block == $domain_name_email ) {
        		$this->errors[] = Tools::displayError('Invalid email address.');

This doesn't work! What is wrong in code or there is another way?

Edited March 20, 2018 by ThisSmart (see edit history)