I would say because your files have an extention only google chrome can read (or along those lines) it looks like.

Try uploading to http://www.postimage.org

mail.google.com/mail/u/0/?ui=2&ik=e021b30f28&view=att&th=158eb1e009c8ae60&a ttid=0.5&disp=safe&realattid=f_iwjv8djf4&zw

vs

example.jpg