Gzip compression is an OWA 2007 option that compresses Web content at the server level before its sent to end users. There are a few things you should know about Gzip.
First, Gzip is enabled by default, but the default compression level is set to Low. Additionally, Gzip can negatively affect your client access server's performance since the server must compress Web content. If you change the Gzip compression level, you'll have to restart IIS before the change takes effect.
Which compression level to use depends on where your biggest performance bottleneck is. If your Internet connection (or your remote user's Internet connection) is the bottleneck, you can improve the end-user experience by setting the Gzip compression level to High.
To do so, open the Exchange Management Shell and enter: Set-OwaVirtualDirectory -Identity "owa (Default Web Site)" -GzipLevel High
However, if there is enough Internet bandwidth, but your client access server is suffering from excessive CPU use you may be able to improve performance by disabling Gzip. To do so, enter: Set-OwaVirtualDirectory -Identity "owa (Default Web Site)" -GzipLevel Off
Reminder: You must restart IIS before your changes will take effect. OWA will be temporarily unavailable during this time. Perform the restart by either rebooting the client access server or by opening a command prompt window and entering:IISRESET /NOFORCE