SMTPDebug = 3;
    $mail->Debugoutput = function($str, $level) {
      foreach(preg_split("/((\r?\n)|(\r\n?)|\n)/", $str) as $line){
        if (empty($line)) { continue; }
        if (preg_match("/SERVER \-\> CLIENT: 2\d\d.+/i", $line)) {
          echo '' . htmlspecialchars($line) . '
';
        }
        elseif (preg_match("/SERVER \-\> CLIENT: 3\d\d.+/i", $line)) {
          echo '' . htmlspecialchars($line) . '
';
        }
        elseif (preg_match("/SERVER \-\> CLIENT: 4\d\d.+/i", $line)) {
          echo '' . htmlspecialchars($line) . '
';
        }
        elseif (preg_match("/SERVER \-\> CLIENT: 5\d\d.+/i", $line)) {
          echo '' . htmlspecialchars($line) . '
';
        }
        elseif (preg_match("/CLIENT \-\> SERVER:.+/i", $line)) {
          echo '' . htmlspecialchars($line) . '
';
        }
        elseif (preg_match("/^(?!SERVER|CLIENT|Connection:|\)).+$/i", $line)) {
          echo '    ↪ ' . htmlspecialchars($line) . '
';
        }
        else {
          echo htmlspecialchars($line) . '
';
        }
      }
    };
    $mail->isSMTP();
    $mail->Host = $hostname;
    if (!empty($username)) {
      $mail->SMTPAuth = true;
      $mail->Username = $username;
      $mail->Password = $password;
      $mail->Port = $port;
    }
    $mail->setFrom($mail_from, 'Mailer');
    $mail->Subject = 'A subject for a SMTP test';
    $mail->addAddress($RELAY_TO, 'Joe Null');
    $mail->Body = 'This is our test body';
    $mail->send();
  }
  else {
    echo "Unknown relayhost.";
  }
}
else {
  echo "Permission denied.";
}