codice:
/* Namespace alias. */
use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;

/* Include the Composer generated autoload.php file. */
require 'C:\xampp\composer\vendor\autoload.php';

/* If you installed PHPMailer without Composer do this instead: */
/*
require 'C:\PHPMailer\src\Exception.php';
require 'C:\PHPMailer\src\PHPMailer.php';
require 'C:\PHPMailer\src\SMTP.php';
*/

/* Create a new PHPMailer object. Passing TRUE to the constructor enables exceptions. */
$mail = new PHPMailer(TRUE);

/* Open the try/catch block. */
try {
   //Enable SMTP debugging.
   $mail->SMTPDebug = 3;                               
   //Set PHPMailer to use SMTP.
   $mail->isSMTP();
   $mail->SMTPAutoTLS = true;
   //Set SMTP host name                          
   $mail->Host = "smtps.pec.aruba.it";
   //Set this to true if SMTP host requires authentication to send email
   $mail->SMTPAuth = true;                          
   //Provide username and password     
   $mail->Username = "areaverde@cert.azienda.it";                 
   $mail->Password = "super_secret_password";                           
   //If SMTP requires TLS encryption then set it
   $mail->SMTPSecure = PHPMailer::ENCRYPTION_SMTPS;                           
   //Set TCP port to connect to
   $mail->Port = 465;
   /* Set the mail sender. */
   $mail->setFrom('darth@empire.com', 'Darth Vader');

   /* Add a recipient. */
   $mail->addAddress('mariorossi@pec.it', 'Emperor');

   /* Set the subject. */
   $mail->Subject = 'Force';

   /* Set the mail message body. */
   $mail->Body = 'There is a great disturbance in the Force.';

   /* Finally send the mail. */
   $mail->send();
}
catch (Exception $e)
{
   /* PHPMailer exception. */
   echo $e->errorMessage();
}
catch (\Exception $e)
{
   /* PHP exception (note the backslash to select the global namespace Exception class). */
   echo $e->getMessage();
}
Così che errore ti stampa?