Question : OWA attachment (docx, xlsx) wants to be saved as zip file.  Why?

Peculiar problem in that this only happens on one computer.  

User is opening an attachment via OWA.  This is an XLSX (also happens with DOCX) file but Internet Explorer insists on saving it as a zipped file.  I can change save as File Type All and add the .xlsx extension and this saves it correctly.  The Internet suggested adding the above extensions in OWAAdmin but why is this happening only on this ONE computer?

Answer : OWA attachment (docx, xlsx) wants to be saved as zip file.  Why?

This problem occurs when the file extension type does not match a known MIME type.   Because Office 2007 was released after IIS6, it doesn't understand the new MIME types for .docx, xlsx, etc from Office 2007

Check out this page for help on configuring them in IIS

http://www.jameskovacs.com/blog/ConfiguringIIS6ToServeOffice2007FileFormats.aspx

Note, you must configure the MIME types identical for forward facing and back end servers for it to resolve this problem and you must restart IIS on any system that did not have the proper MIME types.