保护我的PHP电子邮件表单

Question

我第一次尝试使用PHP而且我正在努力。我不希望任何人劫持我的表单以向其他人发送垃圾邮件。这样做吗？表单是用HTML格式的，当你点击提交时，它会通过POST调用orderform.php

<?php                        <!-- this is orderform.php -->
$to = 'myemail@myemil.com';  <!-- this is my hard coded email address-->
$subject = 'Order Form';

$message = 'First Name: '. filter_var($_POST['first_name']."\n", FILTER_SANITIZE_STRING)
        .'Last Name: '. filter_var($_POST['last_name']."\n", FILTER_SANITIZE_STRING)
        .'Mobile Phone: '. filter_var($_POST['phone']."\n", FILTER_SANITIZE_STRING)
        .'Email: '. filter_var($_POST['email'], FILTER_SANITIZE_EMAIL)."\n"
        .'Date: '. filter_var($_POST['date']."\n", FILTER_SANITIZE_STRING)
        .'Time: '. filter_var($_POST['time']."\n", FILTER_SANITIZE_STRING)
        .'Location: '. filter_var($_POST['location']."\n", FILTER_SANITIZE_STRING)
        .'Special Requests: '. filter_var($_POST['special']."\n", FILTER_SANITIZE_STRING)
    .'Service: '.$_POST['service']."\n"
    .'Package: '.$_POST['package']."\n"
    .'Photo Studio: '.$_POST['studio']."\n"
    .'Makeup: '.$_POST['makeup']."\n"
    .'Photo Editing: '.$_POST['editing'];

mail($to,$subject,$message);
header("Location: success.html");

?>

谢谢！