PHPMailer を使用して Gmail の SMTP サーバー経由でメールを送信できないのはなぜですか?

$mail = new PHPMailer(); // New PHPMailer object
$mail->IsSMTP(); // Enable SMTP protocol
$mail->SMTPDebug = 1; // For debugging (log errors and messages)
$mail->SMTPAuth = true; // Enable SMTP authentication
$mail->SMTPSecure = 'ssl'; // Utilize Secure Socket Layer (SSL) for secure transmission (required for Gmail)
$mail->Host = "smtp.gmail.com";
$mail->Port = 465; // Or 587 depending on server settings
$mail->IsHTML(true); // Allow HTML-formatted emails
$mail->Username = "johndoe@gmail.com"; // Your Gmail username
$mail->Password = "mysecretpassword"; // Your Gmail password
$mail->SetFrom("sender@gmail.com"); // Set sender address
$mail->Subject = "Test Email";
$mail->Body = "Hello from PHPMailer!";
$mail->AddAddress("recipient@gmail.com"); // Add recipient address

if (!$mail->Send()) {
    echo "Mailer Error: " . $mail->ErrorInfo;
} else {
    echo "Email sent successfully!";
}