// Quote: SMF; [SiNaN]
function domain_exists($email, $record = 'MX')
{
	list($user, $domain) = split('@', $email);

	$function = (function_exists('checkdnsrr') ? '' : 'smf_') . 'checkdnsrr';

	return $function($domain, $record);
}

function smf_checkdnsrr($host, $type = '')
{
	if (!empty($host))
	{
		if ($type == '')
			$type = "MX";

		exec("nslookup -type=$type $host", $result);
		foreach ($result as $line)
		{
			if (preg_match('~^' . preg_quote($host) . '~i', $line))
				return true;
		}
		return false;
	}
	return false;
}

// Örnek: domain_exists('ali@ata.bak')