php: contact form

gistfile1.php

<form id="contactForm" method="post">
  <fieldset class="grid halves">
  <div class="grid-item">
	  <ol>
		<li>
		  <label class="label--has-placeholder" for="firstName">First Name</label>
		  <input type="text" placeholder="First Name" name="firstName" id="firstName">
		</li>
		<li>
		  <label class="label--has-placeholder" for="lastName">Last Name</label>
		  <input type="text" placeholder="Last Name" name="lastName" id="lastName">
		</li>
		<li>
		  <label class="label--has-placeholder" for="emailAddress">Email</label>
		  <input class="js-validate-email" type="text" placeholder="Email" name="email" id="emailAddress">
		</li>
		<li>
		  <label class="label--has-placeholder" for="messageText">Text</label>
		  <textarea name="message" placeholder="Text" id="messageText"></textarea>
		</li>
		<li>
		<button class="button button-primary" type="submit">Submit</button>
		</li>
	  </ol>
	</div>
	<!-- .grid-item -->
  </fieldset>
  <!-- .halves -->
  <h3 class="notification"></h3>
</form>
<!-- .form-with-placeholders --> 

<script src="http://code.jquery.com/jquery-1.9.1.js"></script>
<script>	
	$('#contactForm').on('submit', function () {
	    var
			fname = $('[name=firstName]').val(),
	        lname = $('[name=lastName]').val(),
	        email = $('[name=email]').val(),
	        message = $('[name=message]').val();

	    if ($('#contactForm input[type="text"]').val() == "" || $("#contactForm textarea").val() == "") {
	        $('#contactForm input[type="text"],#contactForm textarea').addClass('fielderror');
	    } else {
	        $.ajax({
	            type: "POST",
	            url: "functions.php",
	            data: {
	                fname: fname,
	                lname: lname,
	                email: email,
	                message: message
	            }
	        }).success(function (html) {
	            $('h3.notification').html('Your message has been sent successfuly, we\'ll feed you back as soon as we can. Thank you').addClass('successmsg');
	        }).error(function () {
	            $('h3.notification').html('Oops something went wrong!').addClass('errormsg');
	        });

	        $('#contactForm fieldset').animate({
	            'marginLeft': '800px'
	        }, 300, 'swing', function () {
	            $('#contactForm fieldset').css({
	                'display': 'none',
	                'margin-left': '0'
	            }).html().fadeIn();
	        });
	    }
	    return false;
	});
	$('#contactForm input[type="text"],#contactForm textarea').on('click', function () {
	    $('#contactForm input[type="text"],#contactForm textarea').removeClass('fielderror');
	});
</script>

<?php
  if(isset($_POST['fname']) && isset($_POST['lname']) && isset($_POST['email']) && isset($_POST['message'])) {
		$to  	 = '[email protected]';
		$subject = 'Message from ' . $_POST['fname'] . ' (' .$_POST['email']. ')';
		$message = $_POST['message'];
		$headers = "From: " . $_POST['email'] . "\r\n";

		$sent = mail($to, $subject, $message, $headers);
		
		if($sent) {
			echo '<h2 class="success">Your message has been sent!</h2>';
		} else {
			echo '<h2 class="error">Oops something goes wrong!</h2>';
		}
	}
?>