code: public function getContent(Zend_Mail $mail)
      {
          $hasQueue = $this->hasQueue();
  
          if ($hasQueue && $queue = $this->getQueue()) {
              return $queue->getMessageBody();
          }
  
          /** @var Zend_Mime_Part $mimePart */
          $mimePart = $this->isPlain() ? $mail->getBodyText() : $mail->getBodyHtml();
  
          return $mimePart ? $this->getPartDecodedContent($mimePart) : '';
      }
docs: Returns raw content attached to specified mail object
  
  @param Zend_Mail $mail
  @return string