Ajax enabled feedback form with XML page

I am trying to make an ajax feedback form with a xml page that has a list of email addresses on it. The form should check for nonempty fields as well as checking to see if the email entered is on the xml page. I think I have the form and the xml page done correctly but now I am stuck. Could someone point me in the right direction please and thank you.

XML PAGE


<?xml version="1.0"?>
<address>
	<address>
		<email>bibo@ymail.com</email>
	</address>
		<address>
		<email>stella@ymail.com</email>
	</address>
		<address>
		<email>timster@aol.com</email>
	</address>
</address>

HTML PAGE


<!DOCTYPE html>
<html lang="en">
	<head>
		<script type="text/javascript">
			var asyncRequest;
			
			function clearEmail()
			{
				document.getElementById("address").innerHTML="";
			}
			
			function getEmail(file)
			{
				asyncRequest = new XMLHttpRequest();
				asyncRequest.onreadystatechange = processResponse;
				
				asyncRequest.open("GET", file, true);
				asyncRequest.send(null);
			}
			
			function processResponse()
			{
				if (asyncRequest.readyState == 4 &&
				asyncRequest.status == 200)
				{
					clearEmail();
					
					var address = asyncRequest.responseXML.getElementsByTagName("address");
					
					
					var output = document.getElementById("email");
					
					for (var index = 0; index < address.length; index++)
					{
						var email = address.item(index);
						
						address.appendChild(email);
						output.appendChild(email);
					}
				}
			}
		</script>
	</head>
	<body>
	<header>
		<h1>Register</h1>
	</header>
<div id="form">
     <form id="contact" method="post" action="">
        <label for="name">Your Name:</label>
        <input type="text" name="name" id="name" class="input" />
         </br>
        <label for="email">Your Email:</label>
        <input type="text" name="email" id="email" class="input" />
         </br>
        <label for="message">Message:</label>
        <textarea name="message" id="message" rows="4" cols="40" class="input"></textarea>
          </br>
        <input type="hidden" name="contact" value="1" />
         <button type="submit">Submit!</button>
		 value="address" id="address" onclick="getEmail('address.xml')" />
     </form>
</div>
</body>
</html>