You must insert a line separator (\n) between subheaders and content like this...
--outer Content-Type: text/plain Content-Disposition: inline Content-Description: text-part-1 Some text goes here --outer Content-Type: multipart/mixed; boundary=inner Content-Disposition: attachment Content-Description: multipart-2 --inner Content-Type: text/plain Content-Disposition: inline Content-Description: text-part-2 Some more text here. --inner Content-Type: text/plain Content-Disposition: attachment Content-Description: jpeg-1 <jpeg data> --inner-- --outer--
