code: private function buildBody($body, string $charset): Mime\Message
      {
          if ($body instanceof Mime\Message) {
              return $body;
          }
  
          // If the body is a string, wrap it into a Mime\Part
          if (is_string($body)) {
              $mimePart = new Mime\Part($body);
              $mimePart->type = $body !== strip_tags($body) ? Mime\Mime::TYPE_HTML : Mime\Mime::TYPE_TEXT;
              $body = $mimePart;
          }
  
          $body->charset = $charset;
          $message = new Mime\Message();
          $message->setParts([$body]);
          return $message;
      }
docs: Sets the message body
  @param string|Mime\Part|Mime\Message $body
  @param string $charset
  @return Mime\Message
  @throws Mime\Exception\InvalidArgumentException