如果在验证联系人表单时出现任何错误，应出现警告消息框

如果在提交表单时出现任何错误，应该出现一个警告框。如果正确提交了表单，还应该出现一个消息框。当出现任何错误时，现有代码将我带到其他页面。并且在提交表单时将我带到另一个页面。我需要根据下面给出的代码出现错误的消息框。

<?php
if(isset($_POST['Email'])) {
    // CHANGE THE TWO LINES BELOW
    $email_to = "jay44556677@gmail.com";
    $email_subject = "website html form submissions";

    function died($error) {
        // your error code can go here
        echo "We're sorry, but there's errors found with the form you submitted.<br /><br />";
        echo $error."<br /><br />";
        echo "Please go back and fix these errors.<br /><br />";
        die();
    }
    // validation expected data exists
    if(!isset($_POST['Name']) ||
        //!isset($_POST['last_name']) ||
        !isset($_POST['Email']) ||
        //!isset($_POST['telephone']) ||
        !isset($_POST['Message'])) {
        died('We are sorry, but there appears to be a problem with the form you submitted.');       
    }
    $first_name = $_POST['Name']; // required
    //$last_name = $_POST['last_name']; // required
    $email_from = $_POST['Email']; // required
    //$telephone = $_POST['telephone']; // not required
    $comments = $_POST['Message']; // required
    $error_message = "";
    $email_exp = '/^[A-Za-z0-9._%-]+@[A-Za-z0-9.-]+'.[A-Za-z]{2,4}$/';
  if(!preg_match($email_exp,$email_from)) {
    $error_message .= 'The Email Address you entered does not appear to be valid.<br />';
  }
    $string_exp = "/^[A-Za-z .'-]+$/";
  if(!preg_match($string_exp,$first_name)) {
    $error_message .= 'The First Name you entered does not appear to be valid.<br />';
  }
  //if(!preg_match($string_exp,$last_name)) {
    //$error_message .= 'The Last Name you entered does not appear to be valid.<br />';
  //}
  if(strlen($comments) < 2) {
    $error_message .= 'The Comments you entered do not appear to be valid.<br />';
  }
  if(strlen($error_message) > 0) {
    died($error_message);
  }
    $email_message = "Form details below.'n'n";
    function clean_string($string) {
      $bad = array("content-type","bcc:","to:","cc:","href");
      return str_replace($bad,"",$string);
    }
    $email_message .= "Name: ".clean_string($first_name)."'n";
    //$email_message .= "Last Name: ".clean_string($last_name)."'n";
    $email_message .= "Email: ".clean_string($email_from)."'n";
    //$email_message .= "Telephone: ".clean_string($telephone)."'n";
    $email_message .= "Comments: ".clean_string($comments)."'n";

// create email headers
$headers = 'From: '.$email_from."'r'n".
'Reply-To: '.$email_from."'r'n" .
'X-Mailer: PHP/' . phpversion();
@mail($email_to, $email_subject, $email_message, $headers);  
?>
<!-- place your own success html below -->
Thank you for contacting us. We will be in touch with you very soon.
<?php
}
die();
?>