Dispatcher enable TTL not working

I enabled TTL in dispatcher any file and also set an Expires header to be sent back in the target page

I can see the 'Expires' header in response when i access the page in publisher

but when I access the page using webserver / dispatcher URL, that header is not seen in the response anymore.

Is it removed by the webserver when returning response to the browser?

also even after making this change, no TTL related file is created in the cache folder (besides the cached file for the accessed page)

Is something else to be done to enable this?

Thanks