Test for a valid email address and MX records

// Tests for a valid email address and optionally tests for valid MX records, too.
function is_valid_email($email, $test_mx = false)
{
	if(eregi("^([_a-z0-9-]+)(\.[_a-z0-9-]+)*@([a-z0-9-]+)(\.[a-z0-9-]+)*(\.[a-z]{2,4})$", $email))
		if($test_mx)
		{
			list($username, $domain) = split("@", $email);
			return getmxrr($domain, $mxrecords);
		}
		else
			return true;
	else
		return false;
}