This Windows hosting tutorial will explain how to set HTTP Expires Response Header in IIS 7. This could be useful to leverage browser caching and to improve you ASP.NET site speed. Also, it’s recommended by Google PageSpeed Insights – Setting an expiry date or a maximum age in the HTTP headers for static resources instructs the browser to load previously downloaded resources from local disk rather than over the network.
Configure the expires response header
1.Open IIS Manager and navigate to the level you want to manage.
2.In Features View, double-click HTTP Response Headers.
3.On the HTTP Response Headers page, in the Actions pane, click Set Common Headers.
4.In the Set Common HTTP Response Headers dialog box, select the Expire Web content check box and select the following option:
Select After -> Then, in the corresponding boxes, type an integer and select a time interval at which content expires -> The correct recommended value by Google is: type 7 and select Days.