Gmail で PHPmailer を使用するときに発生する「SMTP Connect() Failed」エラーを解決する方法

<code class="php">require_once 'C:\xampp\htdocs\email\vendor\autoload.php';

define ('GUSER','[email&#160;protected]');
define ('GPWD','your password');

// make a separate file and include this file in that. call this function in that file.

function smtpmailer($to, $from, $from_name, $subject, $body) { 
    global $error;
    $mail = new PHPMailer();  // create a new object
    $mail->IsSMTP(); // enable SMTP
    $mail->SMTPDebug = 2;  // debugging: 1 = errors and messages, 2 = messages only
    $mail->SMTPAuth = true;  // authentication enabled
    $mail->SMTPSecure = 'tls'; // secure transfer enabled REQUIRED for GMail
    $mail->SMTPAutoTLS = false;
    $mail->Host = 'smtp.gmail.com';
    $mail->Port = 587;

    $mail->Username = GUSER;  
    $mail->Password = GPWD;           
    $mail->SetFrom($from, $from_name);
    $mail->Subject = $subject;
    $mail->Body = $body;
    $mail->AddAddress($to);
    if(!$mail->Send()) {
        $error = 'Mail error: '.$mail->ErrorInfo; 
        return false;
    } else {
        $error = 'Message sent!';
        return true;
    }
}</code>