   end
 
   if gen_smtp_major >= 1 do
-    defp attachment_content_params(:inline) do
+    defp attachment_content_params(:inline, filename) do
       %{
         content_type_params: [],
         disposition: "inline",
-        disposition_params: []
+        disposition_params: [{"filename", filename}]
       }
     end
   else
-    defp attachment_content_params(:inline) do
+    defp attachment_content_params(:inline, filename) do
       [
         {"content-type-params", []},
         {"disposition", "inline"},
-        {"disposition-params", []}
+        {"disposition-params", [{"filename", filename}]}
       ]
     end
   end

          format,
          [
            {"Content-Transfer-Encoding", "base64"},
            {"Content-Id", "<#{filename}>"}
            | custom_headers
          ],
          attachment_content_params(:inline),
          content
        }
    end

  end

  defp prepare_attachment(
         %Swoosh.Attachment{
           cid: cid,
           filename: filename,
           content_type: content_type,
           type: attachment_type,
