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