HTML ile Mail Gönderememe problemi ?

<?php
// Import PHPMailer classes into the global namespace
// These must be at the top of your script, not inside a function
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\SMTP;
use PHPMailer\PHPMailer\Exception;

// Load Composer's autoloader
require 'vendor/autoload.php';

// Instantiation and passing `true` enables exceptions
$mail = new PHPMailer(true);

try {
//Server settings
$mail->SMTPDebug = SMTP::DEBUG_SERVER; // Enable verbose debug output
$mail->isSMTP(); // Send using SMTP
$mail->Host = 'smtp1.example.com'; // Set the SMTP server to send through
$mail->SMTPAuth = true; // Enable SMTP authentication
$mail->Username = 'user@example.com'; // SMTP username
$mail->Password = 'secret'; // SMTP password
$mail->SMTPSecure = PHPMailer::ENCRYPTION_STARTTLS; // Enable TLS encryption; `PHPMailer::ENCRYPTION_SMTPS` encouraged
$mail->Port = 587; // TCP port to connect to, use 465 for `PHPMailer::ENCRYPTION_SMTPS` above

//Recipients
$mail->setFrom('from@example.com', 'Mailer');
$mail->addAddress('joe@example.net', 'Joe User'); // Add a recipient
$mail->addAddress('ellen@example.com'); // Name is optional
$mail->addReplyTo('info@example.com', 'Information');
$mail->addCC('cc@example.com');
$mail->addBCC('bcc@example.com');

// Attachments
$mail->addAttachment('/var/tmp/file.tar.gz'); // Add attachments
$mail->addAttachment('/tmp/image.jpg', 'new.jpg'); // Optional name

// Content
$mail->isHTML(true); // Set email format to HTML
$mail->Subject = 'Here is the subject';
$mail->Body = 'This is the HTML message body <b>in bold!</b>';
$mail->AltBody = 'This is the body in plain text for non-HTML mail clients';

$mail->send();
echo 'Message has been sent';
} catch (Exception $e) {
echo "Message could not be sent. Mailer Error: {$mail->ErrorInfo}";