Edge Cache Expiration controls how long to tell the CDN's edge server to cache static resources from your website. The headers set by this setting are not sent to browsers. Generally this should be set to the same value as the Browser Cache Expiration setting.
For the purposes of this setting, a static resource is any resource with one of the following Content-Types or file extensions:
Equivalent Server Headers
If the resource is a static resource and the status code of the response from your server is
200 OK, this setting sets the following headers on the resource:
Surrogate-Control: public, max-age=SETTING_TTL_IN_SECONDS
Otherwise the following headers are set to tell the edge server not to cache the resource:
Surrogate-Control: max-age=0, must-revalidate
If these headers are not appropriate for your use case or want to cache (or not cache) additional content types or status codes, you can set this option to
Respect Existing Headers, and then configure your server to set the appropriate cache headers.