protected function get_email_from_header($message, $header)
    {
        $value = $message->headers->get($header, false);

        if (strtolower($header) == 'received') {
            // find first email address in all Received headers
            $email = null;
            foreach ((array) $value as $entry) {
                if (preg_match('/[\s\t]+for[\s\t]+<([^>]+)>/', $entry, $matches)) {
                    $email = $matches[1];
                    break;
                }
            }

            $value = $email;
        }

        return (array) $value;
    }