Mime type for excel 2007

Question

How can I set the correct MIME type that works with excel 2007? right now I have this:

header("Content-type: application/vnd.ms-excel; charset=UTF-8");

my browser keeps telling me that is a 97 2003 file, but when I try to open the file with excel 2007, the program shows some warning, I can see the document, but I'm trying to avoid that warning.

Answer 1

application/vnd.openxmlformats-officedocument.spreadsheetml.sheet

http://support.microsoft.com/?id=936496