Validating user input against xml

I want to take user input from HTML and validate it against data stored in xml so that the email is unique.

Here's the Javascript

var Email  = document.getElementById("Email").value;
var result = true;

var request = new XMLHttpRequest();
    request.open("GET", "user.xml", false);
    request.send();
    var xml = request.responseXML;
    var xmlEmails = xml.getElementsByTagName("email");
    for(var i = 0; i < xmlEmails.length; i++) {
        var xmlEmail = xmlEmails[i];
        for(var j = 0; j < email.length; j++) {
            if (email == email[j].childNodes[j].nodeValue)
                    {result = false;)                       
        }
    }

Here's the xml file data

<?xml version="1.0"?>
<customers>
<customer>
    <id>0</id>
    <firstname>John</firstname>
    <lastname>Doe</lastname>
    <email>JohnDoe@mia.com</email>
    <password>insecure</password>
</customer>
<customer>
    <id>1</id>
    <firstname>Jane</firstname>
    <lastname>Doe</lastname>
    <email>JaneDoe@mia.com</email>
    <password>forgetful</password>
</customer>
</customers>

Thanks :).