SMTP 接続: 「SMTP Connect() が失敗しました。メッセージは送信されませんでした。」というメッセージが表示されるのはなぜですか?

<code class="php">$mail->IsSMTP();</code>

<code class="php">// require necessary classes
require 'class.phpmailer.php';
require 'class.smtp.php';

// initialize PHPMailer
$mail = new PHPMailer();

// use SMTP
$mail->Mailer = "smtp";

// configure SMTP settings
$mail->SMTPDebug = 2;
$mail->Host = "ssl://smtp.gmail.com";
$mail->Port = 587;
$mail->SMTPAuth = true;
$mail->Username = "[email protected]";
$mail->Password = "mypasswword";
$mail->Priority = 1;

// set email details
$mail->AddAddress("[email protected]", "Name");
$mail->SetFrom($visitor_email, $name);
$mail->AddReplyTo($visitor_email, $name);

// compose email
$mail->Subject = "Message from Contact form";
$mail->Body = $user_message;
$mail->WordWrap = 50;

if (!$mail->Send()) {
  echo 'Message was not sent.';
  echo 'Mailer error: ' . $mail->ErrorInfo;
} else {
  echo 'Message has been sent.';
}</code>