My .docx file opens as a .zip in Outlook Web Access – WTF?

TF is that Exchange 2003 doesn’t know about these new-fangled file extensions so it looks at the headers and sees that they are zip-compressed and assumes they are ZIP files… We just need to add the proper MIME types to Exchange which will in turn set up the attachment properly in OWA.

  1. Open Exchange System Manager
  2. Open the Global Settings branch
  3. Right-click on Internet Message Formats and choose Properties. This brings up the current list of known MIME-types.
  4. Click the Add button. Add the MIME type descriptions (application/vnd.openxmlformats-officedocument.presentationml.presentation) below into the first textbox, and then enter the extension (pptx) in the other textbox.
  5. Click OK and get out of all the dialogs, close ESM.
  6. When you’ve added all 8 of the new MIME-types, restart the Microsoft Exchange Information Store service.


  • application/vnd.openxmlformats-officedocument.presentationml.presentation pptx
  • application/vnd.openxmlformats-officedocument.presentationml.slide sldx
  • application/vnd.openxmlformats-officedocument.presentationml.slideshow ppsx
  • application/vnd.openxmlformats-officedocument.presentationml.template potx
  • application/vnd.openxmlformats-officedocument.spreadsheetml.sheet xlsx
  • application/vnd.openxmlformats-officedocument.spreadsheetml.template xltx
  • application/vnd.openxmlformats-officedocument.wordprocessingml.document docx
  • application/vnd.openxmlformats-officedocument.wordprocessingml.template dotx

After doing this on the server side, close and re-open Internet Explorer and re-login to OWA.  I cleared my cache in between just to be on the safe side and now .docx files download properly.  Yay!

FWIW, when searching for this solution I found a number of people suggesting that these MIME-types needed to be set up in IIS.  They were already there on my system, just not in ESM.  Also, there is this KB article about opening documents in or not in IE here: if that is part of your problem.  Just sayin’.

0 replies

Leave a Reply

Want to join the discussion?
Feel free to contribute!

Leave a Reply

Your email address will not be published. Required fields are marked *