Why cant the mail function for a php contact form be used in MAMP?

<div class="container clearfix">
    <div id="logo" class="grid_4">
        <object data="img/logo.svg" type="image/svg+xml" class="logo">
            <a href="logo.svg" >
                <!--[if lte IE 8 ]-->
                <img src="img/logo.gif" alt="Smells Like Bakin">
                <!--![endif]-->
            </a>
        </object>

    </div>
    <div id="nav" class="grid_8 omega" >
        <ul>
            <li class="about"><a href="#">About</a></li>
            <li class="pricing"><a href="pricing.html">Cupcakes & Prices</a></li>
            <li class="locations"><a href="locations.html">Locations</a></li>
            <li class="contact"><a href="contact.html">Contact Us</a></li>
        </ul>
    </div>

    <div class="grid_12">
        <h1 class="hero">We have a wide variety of delicious desserts that are sure to take you by surprise!</h1>
    </div>


    <div id="form" class="grid_12 omega">
        <h2>Contact Smells Like Bakin'</h2>
        <form action="contact.php" method="POST">

            <p>
                <label for="name">Name:</label>
                <input name="name" id="name" type="text" class="required">
                <span>Please enter your name</span>
            </p>

            <p>
                <label for="email">Email:</label>
                <input name="email" id="email" type="text" class="required"> 
                <span>Please enter a valid email address</span>
            </p>

            <p>
                <label for="subject">Subject:</label>
                <input name="subject" id="subject" type="text"> 
                <span>Please enter your subject</span>
            </p>

            <p>
                <label for="message">Message</label>
                <textarea name="message" id="message" class="required"></textarea> 
                <span>Please enter your message</span>
            </p>
            <p class="submit">
                <input type="submit" value="Submit" class="btn-submit">
            </p>
        </form>


    </div>



    <div id="footer" class="grid_12">
        <div id="about" class="grid_7">
            <h2>Inside the Kitchen</h2>
            <p>Smells Like Bakin’ started out in the garage of the husband wife duo Allison &amp; Joseph. Allison is the baker, and Joseph found a way for them to make a business out of her tasty treats. Flash forward to today and they have a successful store front, catering business and cupcake truck. </p>
            <p><a href="#" class="btn-small">Read More</a></p>
        </div>


        <div id="contact" class="grid_5 omega">
            <h2>Get Bakin’ with Us</h2>
            <p>Call us: <span class="contact">1-800-CUP-CAKE</span><br>
                Email us: <a href="#">bakeon@smellslikebakin.com</a></p>

                <p>We announce all of our new flavors first through Facebook &amp; Twitter, and even take requests!</p>     

                <object data="img/facebook.svg" type="image/svg+xml">
                    <a href="facebook.svg">
                        <!--[if lte IE 8 ]-->
                        <img src="img/facebook.gif" alt="Facebook">
                        <!--![endif]-->
                    </a>
                </object>

                <object data="img/twitter.svg" type="image/svg+xml">
                    <a href="twitter.svg">
                        <!--[if lte IE 8 ]-->
                        <img src="img/twitter.gif" alt="Twitter">
                        <!--![endif]-->
                    </a>
                </object>
            </div>

            <div id="copyright" class="grid_12">
                <p>© 2012 Smells Like Bakin' Cupcake Company. All Rights Reserved.</p>
            </div>

        </div>

    </div>

    <script type="text/javascript" src="js/jquery.js"></script>
    <script type="text/javascript" src="js/validEmail.js"></script>
    <script type="text/javascript">
        var $submit = $(".submit input");
        var $required = $(".required");
        function containsBlanks(){
            var blanks = $required.map(function(){ return $(this).val() == "";});
            return $.inArray(true, blanks) != -1;
        }

        function requiredFilledIn(){
            if(containsBlanks() || !$("#email").validEmail()) 
                $submit.attr("disabled","disabled");
            else 
                $submit.removeAttr("disabled");
        }

        $("#form span").hide();
        $("input,textarea").focus(function(){
            $(this).next().fadeIn("slow");
        }).blur(function(){
            $(this).next().fadeOut("slow");
        }).keyup(function(){
            //Check all required fields.
            requiredFilledIn();
        });

        $("#email").validEmail({on:"keyup", success:function(){
            $(this).next().removeClass("error").addClass("valid");
        }, failure:function(){
            $(this).next().removeClass("valid").addClass("error");
        }});

        requiredFilledIn();
    </script>
</body>
</html>

$to_email = "jhallpilot@gmail.com";

$name = $_POST["name"];
$email = $_POST["email"];
$message = $_POST["message"];

$subject = "[Contact Form] " . $_POST["subject"];


function isValidEmail($email) {
    return strpos($email, "@") !== false;
}

if($name != "" && $email != "" && $message != "" && isValidEmail($email)) {

$full_message = "Name : ". $name . "\n";
$full_message .= "Email : ". $email . "\n";
$full_message .= "Message :\n\n". $message . "\n";

mail($to_email, $subject, $full_message);
header("location: contact.html");
exit();