Mailer SMTP Error: Could not connect to SMTP host บนเซิฟเวอร์จริง แต่บน localhost ส่งได้

<?php

require_once('class.phpmailer.php');

$name = $_POST[name];
$email = $_POST[email];
$phone=$_POST[phone];
$city=$_POST[city];
$question = $_POST[message];

$mail = new PHPMailer();
$mail->CharSet="utf-8";
$mail->IsHTML(true);

$mail->IsSMTP();
$mail->SMTPAuth = true; 
$mail->SMTPSecure = "ssl";
$mail->Host = "smtp.gmail.com"; 
$mail->Port = 465; 
$mail->Username = "******@gmail.com";
$mail->Password = "*********"; 
$mail->From = $email; 
$mail->FromName = $name;

$mail->Subject = "ข้อความจากผู้ติดต่อทางเว็บไซต์";
$mail->Body = "จากคุณ : ".$name."&nbsp;&nbsp;"."จังหวัด : ".$city."<br/>"."เบอร์โทรศัพท์ : ".$phone."<br/>"."E-mail : ".$email."<hr/>".$question;

$mail->AddAddress("*******@*******.com"); // to Address
$mail->set('X-Priority', '1'); //Priority 1 = High, 3 = Normal, 5 = low

if (!$mail->Send()) {
    echo "Mailer Error: " . $mail->ErrorInfo;
} else {
    echo "<script>
        alert('Ok')
        window.location.href='contact-us.html';
        </script>";
}
?>