Improve Outlook Web Access Performance
It is possible to reduce traffic and resources on the computer running Exchange by increasing the time until expiration of static files from the <root>\Program Files\Exchsrvr\Exchweb\Controls and <root>\Program Files\Exchsrvr\Exchweb\Img directories. These static files include all the .gif icons, tool bars, windows for display of messages, and other fixtures of Outlook Web Access required by the client computers' browsers.
The browser receives items stored in these directories on the Exchange server, and then stores them in the browser cache until they expire. When the browser detects that the expiry time on an item has passed, Outlook Web Access will send a request to the server for an updated version, along with a "modified since" header containing the time the browser cached the original item. If the item has not been modified since it was originally cached, the browser will continue using the item stored in its cache and the server will essentially reset the expiry time. If the item has been modified, the server will return the new item and the browser will not use the cached item. The new item, with a new expiry time, will then replace the old item in the cache.
By default, these files are marked as expiring in one day when they are received from the server by the browser; thus, once each day, each user will request and receive these files from the server. Except in cases where "static" content is modified to include system messages or advertisements, these files will not change except possibly in the event of a future Exchange service pack installation. Increasing the time before expiration to a month or a year (or setting the content to not expire) may make better use of system resources.
Caution Keep in mind, however, that increasing the expire time means the client computer will not be sending any requests to the server during that time. Instead, the client computer will use only cached items. This situation occurs because the browser first checks the expiry time of a cached item and will only request a new file if the present time exceeds the expiry time. If the present time does not exceed the expiry time, the client computer does not bother to check for a modified file on the server. If an Exchange administrator makes any modifications during this period, the client computer will have no way of knowing about the changes.To change the expiry settings for items in the Controls and Img directories:
Tip To force the browser to refresh the entire contents on a page, thus ignoring data in the cache, press CTRL+SHIFT, and then click Refresh.