我正试图用PHPMailer发送电子邮件。这是我发送电子邮件的功能。它在Ubuntu 14.04的localhost上运行良好。

function smtpMail($to, $from, $from_name, $subject, $body) {
   $mail = new PHPMailer;
   $mail->IsSMTP();                                      // tells PHPMailer to use SMTP
   $mail->Host       = gethostbyname('smtp.gmail.com');  // sets the hostname of the mail server
   $mail->Port       = 587;                              // sets the SMTP port number
   $mail->SMTPSecure = 'tls';                            // sets the encryption system to use
   $mail->SMTPDebug  = 2;                                   // debug level
   $mail->SMTPAuth   = true;                             // whether to use SMTP authentication
   $mail->Username   = 'jdoe@company.org';            // username to use for SMTP authentication
   $mail->Password   = 'qwerty';                     // password to use for SMTP authentication
   $mail->CharSet    = 'UTF-8';
   $mail->IsHTML(true);
   $mail->setFrom($from, $from_name);                    // sets who the message is to be sent from
   $mail->Subject = $subject;
   $mail->Body = $body;
   $mail->AddAddress($to);
   if (!$mail->Send ()) {
           return 'Mail error: ' . $mail->ErrorInfo;
           //return 'KO';
   }
   return 'OK';
}

现在我正在尝试将其部署到服务器上。代码是相同的，但它不再工作了。服务器是运行在debian 8.2中的apache2。PHPMailer打印这些行。

2015-12-09 13:35:41 SERVER -> CLIENT: 220 2.0.0 Ready to start TLS
2015-12-09 13:35:41 SMTP Error: Could not connect to SMTP host.
2015-12-09 13:35:41 CLIENT -> SERVER: QUIT
2015-12-09 13:35:41 SERVER -> CLIENT:
2015-12-09 13:35:41 SMTP ERROR: QUIT command failed:

在服务器上，以下命令工作正常：

dig smtp.gmail.com
ping smtp.gmail.com
telnet smtp.gmail.com

我试图用telnet发送电子邮件，它也在工作。我遵循了这个教程（抱歉是法语）我做错了什么？