ASP.NET, Pagespeed and the content-encoding header

Question

I have a very small static site (http://www.codeinside.eu/) and tested it via Google Pagespeed. It told me I should use compression for the page and all JS/CSS files - but here is my problem: I thought that my website is already running with compression. The website is running on Windows Azure Websites and is based on ASP.NET. For CSS/Javascript I use the builtin Bundling feature and the Website should run in release mode - so bundling and minification works fine and as far as I know IIS8 should compress dynamic content.

Then I tried another testing instrument http://www.whatsmyip.org/http-compression-test/ which said that my site is compressed.

My website and several other websites running ASP.NET and IIS (including stackoverflow.com) don't include the "content-encoding:gzip" header in the response - is this a problem with the Pagespeed analyser or is this a problem of IIS? Or is this no problem at all because the header is not that important?

Edit: Of course the browser sends the "accept-encoding:gzip" header in the request.

Answer 1

Found the solution for this issue: We use the Microsoft TMG as a Proxy in our company and it seems to remove the "Content-Encoding" header (and other magic stuff). I was confused because some pages like twitter.com are served to my PC with the "content-encoding: gzip" header and other without any "Content-Encoding" header.
My wild guess: The TMG is case sensitive and only looks for "Content-Encoding", that's why I receive some requests with it and some without it.

So - compression with the correct header works as expected.