On Google Webmaster Guidelines I see this:
"Make sure your web server supports the If-Modified-Since HTTP header. This feature allows your web server to tell Google whether your content has changed since we last crawled your site. Supporting this feature saves you bandwidth and overhead."
I contacted Godaddy and they told me:
"I understand you would like to know if your server currently has the "If-Modified-Since HTTP header" installed. I used an external tool to test this and found that it is not currently being utilized by your server. Additionally I was unable to find a reliable source to get specific requirements on what this server needs to function. In order to determine if your server supports this you will need to provide us the exact specifications required to run it."
How do I ensure the If-Modified-Since HTTP header is supported and that it is active?