Ajax code to call another application page - Mail sending from Javascript to ASPX

function frm_sendmail() {

        if (document.getElementById("first_name").value == "") {

            alert("Please provide your first name");

            document.getElementById("first_name").focus();

            return false;

        }

        if (document.getElementById("last_name").value == "") {

            alert("Please provide your last name");

            document.getElementById("last_name").focus();

            return false;

        }

        if (document.getElementById("email").value == "") {

            alert("Please provide your email address");

            document.getElementById("email").focus();

            return false;

        }

        else {

            if (/^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,3})+$/.test(document.getElementById("email").value)) {

                document.getElementById("txtHint").innerHTML = '<span align="center"><img src="links/images/img16.gif"border="0" /></span>';

                var xmlhttp;

                if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari

                    xmlhttp = new XMLHttpRequest();

                }

                else {// code for IE6, IE5

                    xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");

                }

                xmlhttp.onreadystatechange = function () {

                    // alert('hello'+' '+xmlhttp.readyState+' '+xmlhttp.status);

                    if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {

                        // alert(xmlhttp.responseText);

                        // document.getElementById("txtHint").innerHTML = xmlhttp.responseText;

                    }

                }

                first_name = document.getElementById("first_name").value;

                last_name = document.getElementById("last_name").value;

                email = document.getElementById("email").value;

                to_email = document.getElementById("to_email").value;

                subject = document.getElementById("subject").value;

                xmlhttp.open("POST", "smtpmail/Default.aspx?first_name=" + first_name + "&last_name=" + last_name + "&email=" + email + "&to_email=" + to_email + "&subject=" + subject, true);

                xmlhttp.send();

                close_popup('close_seat');

                alert('Thank you for your sign up request. We will contact you shortly.');

            }

            else {

                alert("Incorrect email address format");

                document.getElementById("email").focus();

                return false;

            }

        }

    }