JQuery Validation - Validate Email Using AJAX Call

I have an invitation form that should only accept emails handled by GMail. I'm trying to plug in asynchronous validation, but not sure what should be returned from the server and w

Solution 1:

problem solved.

Javascript code:

$('#invite').validate({
    rules: {
        email: {
            required: true,
            email: true,
            remote: {
                url: '/admin/isgmail/',
                type: 'POST',
                dataType: 'json',
                data: {
                    email: function() {
                        return $('#email').val();
                    }
                }
            }
        }
    },
    messages: {
        email: "GMail email is required."
    },
    onkeyup: false
});

invite.php should return string "true" if validation is successful, string "false" if there was an error OR JSON-encoded string describing the error: echo json_encode('This is not a Google account');.