Enviar e-mail con autenticación de SMTP con PHPMailer en Windows Server

<?php
 require 'phpmailer\PHPMailer.php';
 require 'phpmailer\SMTP.php';
 require 'phpmailer\Exception.php';

 $mail = new PHPMailer\PHPMailer\PHPMailer();

 $mail->IsSMTP(); // Set mailer to use SMTP
 //$mail->SMTPDebug = 3;
 $mail->Host = 'server-hostname'; // Specify main server name of your account
 $mail->Port = 587; // Set the SMTP port (25/587/465)
 $mail->SMTPAuth = true; // Enable SMTP authentication
 $mail->Username = 'mail@domainname'; // SMTP username
 $mail->Password = '********'; // SMTP password
 $mail->SMTPSecure = 'tls'; // Enable encryption, 'ssl' also accepted

 $mail->From = 'mail@domainname';
 $mail->FromName = 'Your From name';
 $mail->AddAddress('mail@yourdomainname', 'Name'); // Add a recipient
 $mail->IsHTML(true); // Set email format to HTML

 $mail->Subject = 'Here is the subject';
 $mail->Body = 'This is the HTML message body';
 $mail->AltBody = 'This is the body in plain text for non-HTML mail clients';

 if(!$mail->Send()) {
   echo 'Message could not be sent.';
   echo 'Mailer Error: ' . $mail->ErrorInfo;
   } 
  else {
   echo 'Message has been sent';
 }
?>