      [
        {"Content-Type", "text/#{subtype_string}; charset=\"utf-8\""},
        {"Content-Transfer-Encoding", transfer_encoding}
-     ],
-     [
-       {"content-type-params", [{"charset", "utf-8"}]},
-       {"disposition", "inline"},
-       {"disposition-params", []}
-     ], content}
+     ], @content_params, content}
   end
 
   defp add_content_type_header(headers, value) do

            {"Content-Transfer-Encoding", "base64"}
            | custom_headers
          ],
          [
            {"disposition", "attachment"},
            {"disposition-params", [{"filename", filename}]}
          ],
          content
        }


  end

  defp prepare_part(_subtype, nil, _config), do: nil

  @content_params if(gen_smtp_major >= 1,
                    do: %{
                      content_type_params: [{"charset", "utf-8"}],
                      disposition: "inline",
                      disposition_params: []
                    },
                    else: [
                      {"content-type-params", [{"charset", "utf-8"}]},
                      {"disposition", "inline"},
                      {"disposition-params", []}
                    ]
                  )

  defp prepare_part(subtype, content, config) do
    subtype_string = to_string(subtype)
