Apache Config Mime Types: xlsx files are being interpreted as zip files on download, why?

Question

Background: For some reason, whenever a user tries to open an xslx (excel 2007) file from our intranet using MSIE, the file download dialog interprets it as a "zip" file.

Admittedly, xslx files really are zip files, but we don't want that behavior. Just open in Excel, please.

Question:

Firefox, OTOH, opens the files normally. Is it possible that the fault is my apache configs? or is this a client-browser-only issue?

Answer 1

The reason is IE's strange MIME sniffing behaviour: http://msdn.microsoft.com/en-us/library/ms775147.aspx. It basically tries to determine to the file type of a file by looking into its contents, somehow like Linux's file tool.

Answer 2

You must add some new MIME-TYPES on the web-server-side.

See the comment-thread on this windowsnerd.com page (from 2009):

Add this to a .htaccess file and throw it on your site: AddType application/vnd.openxmlformats .docx .pptx .xlsx .xltx . xltm .dotx .potx .ppsx

Should fix many of the problems.

Alternatively, you can add this to the mime.types file located in the config directory of your Apache web server

application/vnd.ms-word.document.macroEnabled.12 .docm
application/vnd.openxmlformats-officedocument.wordprocessingml.document docx
application/vnd.openxmlformats-officedocument.wordprocessingml.template dotx
application/vnd.ms-powerpoint.template.macroEnabled.12 potm
application/vnd.openxmlformats-officedocument.presentationml.template potx
application/vnd.ms-powerpoint.addin.macroEnabled.12 ppam
application/vnd.ms-powerpoint.slideshow.macroEnabled.12 ppsm
application/vnd.openxmlformats-officedocument.presentationml.slideshow ppsx
application/vnd.ms-powerpoint.presentation.macroEnabled.12 pptm
application/vnd.openxmlformats-officedocument.presentationml.presentation pptx
application/vnd.ms-excel.addin.macroEnabled.12 xlam
application/vnd.ms-excel.sheet.binary.macroEnabled.12 xlsb
application/vnd.ms-excel.sheet.macroEnabled.12 xlsm
application/vnd.openxmlformats-officedocument.spreadsheetml.sheet xlsx
application/vnd.ms-excel.template.macroEnabled.12 xltm

http://www.webdeveloper.com/forum/showthread.php?t=162526