Office 2007 introduced new file formats for common document types (Word documents, Excel spreadsheets, and PowerPoint presentations), and has standardized on new MIME types for each new format. The following information is provided to document the new MIME types and their proper use in HTTP content streaming situations.
The following table documents the HTTP MIME types that are available when working with Office 2007 documents:
To fully support the new types, web server administrators are advised to add the MIME types for the Open XML formats to their web server metabase settings so as to add the correct MIME type header in documents saved directly on the server and sent back. For Windows 2003 Servers running IIS 6.0, you can add the Open XML types in IIS Manager, Server Properties, MIME Types. These new formats are included in Windows 2008 running IIS 7.0 by default. For more details on the default MIME types for IIS, please see the following KB article:
936496: Description of the default settings for the MimeMap property and for the ScriptMaps property in IIS
Clients that install Office 2007 or the Office 2007 File Format Compatibility Pack will get client-side MIME mappings to these formats by default.
To use the MIME type in your ASP/ASP.NET code, you should use the built-in Response.ContentType property and set it to the MIME value that matches the content type you are providing. If you fail to set the correct type, security checks by the client may prevent the content from being opened or may prompt the user with an alert that the file is not in the correct format.