IIS is smart enough to add the expiration header only to static content.
It automatically adds the header to images and css files, without touching
the aspx pages.
But, like the author of the post, I am also wonder , how does IIS determine what extensions fall under static content? Is
there a way to modify this list?
Custom Headers:
Remove the X-Powered-By: ASP.NET header. You really don't need it unless you want to attach Visual Studio Remote Debugger to your IIS. Otherwise, it's just sending 21 bytes on every response.
Add "From" header and set the server name. I do this on each webserver and specify different names on each box. It's handy to see from which servers requests are being served. When you are trying to troubleshoot load balancing issues, it comes handy to see if a particular server is sending requests.
Also turn on IIS 6.0 gzip compression. Note that enabling in IIS 6.0 in the Properties, Service tab is not good enough.
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