@PHP邮件发件人中的.SYNTAX-ERROR

我使用HTML表单通过ajax将输入转发到PHP文件，在该文件中使用PHPMailer发送电子邮件。在数据发送到PHP文件之前，我使用JQuery来验证一些输入（名称和邮件地址）。

这是我的代码：

HTML表单：

<form class="ajax" action="script/send_form.php" method="post">
        <input id="name" name="name" type="text"  />
        <input id="mail" name="mail" type="text"  />
        <input id="mail" name="note" type="text"  />
        <button type="submit" id="send">Send</button>
</form>

使用PHPMailer:的自动加载功能的PHP文件

    <?
$return = chr(13).chr(10);
$line = "-----------------------------------------------".$return;
$name = '';
$email = '';
if(!empty($_POST['name'])) {
    $name = $_POST['name'];
}
$email = $_POST['mail'];
$note = $_POST['note'];
$msg = $note;
require 'phpmailer/PHPMailerAutoload.php';
//Create a new PHPMailer instance
$mail = new PHPMailer;
$mail->CharSet = 'UTF-8';
//Set who the message is to be sent from
$mail->From = $email;
$mail->FromName = $name;

//Set who the message is to be sent to
$mail->addAddress('info@internet.com', 'John Doe');
//Set the subject line
$mail->Subject = 'Some Subject';

$mail->Body = $msg;
//send the message, check for errors
if (!$mail->send()) {
    echo "Mail Error: " . $mail->ErrorInfo;
} else {
    echo "Sent";
}
?>

Jquery：

   function validateEmail(email) { 
    var re = /^(([^<>()[']''.,;:'s@'"]+('.[^<>()[']''.,;:'s@'"]+)*)|('".+'"))@(('[[0-9]{1,3}'.[0-9]{1,3}'.[0-9]{1,3}'.[0-9]{1,3}'])|(([a-zA-Z'-0-9]+'.)+[a-zA-Z]{2,}))$/;
    return re.test(email);
}
function validate(){
    var email = $("#mail").val();
      if (validateEmail(email)) {
          var mail = $('#mail').val();
      } else {
  alert ('Bitte gültite E-Mail Adresse eingeben!') 
      }
}
function dottedButton () {
  document.getElementById('send').innerHTML = '...';
} 

$('form.ajax').on('submit', function(ev){
     ev.preventDefault();
     validate ();
     var name = $('#name').val();
     var mail = $('#mail').val();
     if(name && mail){
            var that = $(this);
                url = that.attr('action');
                type = that.attr('method');
                contents = that.serialize();
        dottedButton ();
            $.ajax({
                url: url,
                type: type,
                data: contents,
                success: function(response){
                    document.getElementById('send').innerHTML = 'sent';
                }
            });
     } else {
        alert ('pleas fill out all fields!') 
     };
    return false;
});

问题是：每隔一到两天，我的收件箱里就会有一封空邮件，发件人的电子邮件地址写着：@.SYNTAX-ERROR.

我不知道为什么会发生这种事。可能有些机器人会自动终止PHPMailer吗？

BTW：我的主持人是的hoststar.at

提前感谢！