/**
  * Parses the headers of the provided message
  * @param zibo\library\mail\Message $message The message to parse the headers of
  * @return null
  */
 private function parseHeaders(Message $message)
 {
     $this->headers[self::HEADER_MIME_VERSION] = self::HEADER_MIME_VERSION . ': 1.0';
     $messageId = $message->getMessageId();
     if ($messageId) {
         $this->headers[self::HEADER_MESSAGE_ID] = self::HEADER_MESSAGE_ID . ': ' . $messageId;
     }
     $inReplyTo = $message->getInReplyTo();
     if ($inReplyTo) {
         $this->headers[self::HEADER_IN_REPLY_TO] = self::HEADER_IN_REPLY_TO . ': ' . $inReplyTo;
     }
     $references = $message->getReferences();
     if ($references) {
         $this->headers[self::HEADER_REFERENCES] = self::HEADER_REFERENCES . ': ' . implode(' ', $references);
     }
     $autoSubmitted = $message->getAutoSubmitted();
     if ($autoSubmitted) {
         $this->headers[self::HEADER_AUTO_SUBMITTED] = self::HEADER_AUTO_SUBMITTED . ': ' . $autoSubmitted;
     }
 }