Opening ppt. or pptx file from e-mail

I am trying to open ppt. or pptx. files from my e-mail. I have the keynote app installed on my iPad. When I veiw the e-mail that has either a ppt. or pptx file in it and press the attachment i just get an error message saying 'mail cannot open this attachment'. The ppt. file seems to show up in the e-mail as a 'winmail.dat' don't know if the mail program is converting it or just recognizing it incorrectly. What do I need to do to open these files, which I thought keynote was supposed to suport.
Thanks