Adobe Campaign Classic v7
Static images hosted by Adobe are not served with cache control header directives. Consequently, the image is served each time different clients read the email from ACC server, which is not optimal. A cache control directive could get the image from the cache of a reverse/proxy server.
This issue can be addressed by updates to the infrastructure; for example, there is an option to cache a folder on AWS side. On-premise customers can research additional options on their own.