We’ve updated the Publisher’s Guide (http://blogs.msdn.com/rssteam/articles/PublishersGuide.aspx) with how IE7 detects if a file is a feed. If you publish feeds, make sure that your site’s feed is detected and readable in IE7.
When a user clicks on a link to a feed, IE7 uses the MIME Content-Type information to determine if it is a feed. Here is a list of recommended MIME Content-Types:
RSS 2.0 (.91 and .92): use text/xml (recommended) or application/rss+xml
Atom 1.0: use application/atom+xml
RSS 1.0: use application/xml or text/xml
For generic Content-Types (ex: “text/xml” and “application/xml”) IE7 reads the file and looks for specific strings to determine if it is a feed. For details, please read the Publisher’s Guide.