I am using W3 Total Cache and I got:
Set expires header Set the expires header to encourage browser caching of files. Expires header lifetime: seconds Set cache control header Set pragma and cache-control headers to encourage browser caching of files. Cache Control policy: Set entity tag (eTag) Set the Etag header to encourage browser caching of files. Set W3 Total Cache header Set this header to assist in identifying optimized files. Enable HTTP (gzip) compression Reduce the download time for text-based files.
All those options selected. But I am still getting the issue with:
Specify a cache validator
I am not sure why this is happening and how to fix this?