Emailed Microsoft Office 2007/2010 Files Become ZIP Files

Introduction

I've had a number of work colleagues puzzled with regard to receiving ZIP files in their email from persons who originally sent Microsoft Word documents.  Neither the sender nor the recipient understood how it came about that a Microsoft Word file drafted in Microsoft Word 2007/2010 morphed into a ZIP file on being sent to a coworker.  The answer is interesting.  This is actually an old topic, but one that continues to crop up, so I've collated here a few notes that I have sent to my coworkers on this subject.  The references listed below provide additional technical detail on this topic.

Discussion

Microsoft dramatically changed the latent format of its Office 2007 suite of tools from the previous Office 2003 formats.  Office 2007 applications formats are entirely XML-based and are not a single file but a suite of files.  That's right.  A DOCX or XLSX file is no longer a single file, but is actually a group of files within a single compressed container - the DOCX or XLSX, etc.  And the container is in ZIP format.  The files in the suite each contain the different aspects of the original DOCX content, such as embedded video, sound, charts, writing, styles, footnotes, settings, footer etc [1].  You can see this for yourself by performing the following quick test:

1. Save a Microsoft Word 2007/2010 document in its current format (DOCX).
2. Once the document is saved, change the file ending of this document from DOCX to ZIP.
3. Double-click the ZIP file to explore its contents.

In other words, an Office 2007/2010 file is actually a ZIP container of files that is re-assembled by Office into the appropriate document, when you open that document in an Office product.

These newer Office formats are obviously not recognized by older Exchange server systems, which will not recognize the new DOCX, XLSX, etc endings and instead will detect the file for what it is: a ZIP container [2-7].  If you should receive an Office 2007/2010 file that has ZIP for a file ending, don't despair.  Simply save the ZIP to your machine and then change the file ending back to what it should be (DOCX, XLSX, etc), and you will then be able to open it normally.  Though Exchange may change the file ending, it does not change the content of the file.  There's no need to make any complex configuration changes either on the sender's end or the receiver's.  Just remember to change the file ending back to its appropriate one, on saving it to your machine.

Fortunately, the fix to Microsoft Exchange is well-understood and documented [5-7].  Additionally, if you are still working with an earlier version of Office (2000, 2003), there are freely available resources to enable you to view and work with newer Office version documents [8, 9].  Happy computing!

References

1. Introducing the Office (2007) Open XML File Formats, MSDN Library Technical Articles Office 2007, 5/2006
2. Why would Office 2007 documents only open as a ZIP file, Ask MetaFilter, 9/26/2007
3. Office 2007 Docs in Exchange 2003, Jeff Sheen, Blog post, 4/7/2008
4. OWA 2003, Office 2007 files .xlsx, .docx being saved at .zip, Microsoft Technet Forums, Exchange Server, 6/15/2009
5. Exchange 2003 OWA Not Opening Office 2007 File Attachments, David, Experts Exchange, 12/21/2010
6. Register the 2007 Office system file format MIME types on servers, Microsoft TechNet Library, 7/23/2008
7. Register Office 2007 file format MIME types on servers, Microsoft Office IT Pro Blog Springboard Series, 6/30/2009
8. Microsoft Office Compatibility Pack for Office 2007, Microsoft Your Digital Life
9. How to open and save Word, Excel, and PowerPoint 2007 or 2010 files in earlier versions of Office programs, Microsoft Support, Knowledgebase Article 924074, 8/25/2010

Notes

• None