 * MimeTreeParser::MessagePartList
  * MimeTreeParser::MimeMessagePart
   * MimeTreeParser::TextMessagePart
    * MimeTreeParser::MessagePart
   * MimeTreeParser::EncapsulatedRfc822MessagePart
    * MimeTreeParser::EncryptedMessagePart
     * MimeTreeParser::SignedMessagePart
      * MimeTreeParser::TextMessagePart
       * MimeTreeParser::MessagePart
