php - PHP から HTML メールを送信する

Question

MYSqL は問題なく動作しますが、なぜメールが届かないのですか?

<?php
    //include the connection file

    require_once('connection.php');

    //save the data on the DB and send the email

        if(isset($_POST['action']) && $_POST['action'] == 'submitform')
        {
        //recieve the variables

        $name = $_POST['name'];
        $email = $_POST['email'];
        $url = $_POST['url'];
        $comment = $_POST['comment'];
        $ip = gethostbyname($_SERVER['REMOTE_ADDR']);

        //save the data on the DB

        mysql_select_db($database_connection, $connection);

        $insert_query = sprintf("INSERT INTO contacts (name, email, url, comment, date, ip) VALUES (%s, %s, %s, %s, NOW(), %s)",
                            sanitize($name, "text"),
                            sanitize($email, "text"),
                            sanitize($url, "text"),
                            sanitize($comment, "text"),
                            sanitize($ip, "text"));

        $result = mysql_query($insert_query, $connection) or die(mysql_error());

        if($result)
        {
            //send the email

            $to = "email@aol.com";
            $subject = "message from website";

            //headers and subject
            $headers  = "MIME-Version: 1.0\r\n";
            $headers .= "Content-type: text/html; charset=iso-8859-1\r\n";
            $headers .= "From: ".$name." <".$email.">\r\n";

            $body = "New contact<br />";
            $body .= "Name: ".$name."<br />";
            $body .= "Email: ".$email."<br />";
            $body .= "Comment: ".$comment."<br />";
            $body .= "IP: ".$ip."<br />";

            mail($to, $subject, $body, $headers);

            //ok message

            echo "Your message has been sent";
        }
        }

        function sanitize($value, $type) 
        {
        $value = (!get_magic_quotes_gpc()) ? addslashes($value) : $value;

        switch ($type) {
        case "text":
          $value = ($value != "") ? "'" . $value . "'" : "NULL";
          break;    
        case "long":
        case "int":
          $value = ($value != "") ? intval($value) : "NULL";
          break;
        case "double":
          $value = ($value != "") ? "'" . doubleval($value) . "'" : "NULL";
          break;
        case "date":
          $value = ($value != "") ? "'" . $value . "'" : "NULL";
          break;
        }

        return $value;
    }
?>