    # File lib/vmail/message_formatter.rb, line 13
        def list_parts(parts = (@mail.parts.empty? ? [@mail] : @mail.parts))
          if parts.empty?
            return []
          end
          lines = parts.map do |part|
            if part.multipart?
              list_parts(part.parts)
            else
              # part.charset could be used
              "- #{part.content_type}"
            end
          end
          lines.flatten
        end