New extensions need new MIME types?

[Steve Rindsberg]

The new version of MS Office comes with some new file types/file extensions. I'm wondering whether that'll create new problems for web server administrators and users.

A user on another forum reported that when she opens a .PPTX (Office 2007/PowerPoint) file she created and saved on her own computer, all's well. But when she opens a file someone else sent her, Windows Exporer treats it as a ZIP file.

"Opens" might mean any of several things; we're trying to get her to give us specifics, and it may have nothing whatever to do with web sites/servers. Time will tell.

But one other member asked whether the files from someone else had been posted to a web site, thinking that the mime type may not have been correctly set for PPTX files.

Which got me wondering: what *would* happen if the web server doesn't know what a .PPTX file is. Would it just tell the browser "Beats me, man. Here. You figure it out."

And might the browser look for file signatures of some sort? Since PPTX files are, in fact, ZIP archives, it'd find a file sig for ZIP, in this case.