PHP Send Mail ทดสอบส่งเมลล์ด้วย PHP แล้วไม่ได้รับเมลล์ค๊ะ

        $to = $sql = "SELECT email FROM users WHERE name = '$member_username'";;
	$subject = "Message.";
        $message = " Test ";
        $headers  = 'MIME-Version: 1.0' . "\r\n"; 
        $headers .= 'Content-type: text/html; charset=iso-8859-1' . "\r\n"; 
        $headers .= "From:[email protected]\r\n"; 
        mail($to, $subject, $message, $headers);