Received an email [Improving Cache Strategy for Your AEM as a Cloud Service Solution] use Cloud Services

We have received an email with the subject "[Improving Cache Strategy for Your AEM as a Cloud Service Solution]."

However, I haven't made any changes to the cache rules in dispatcher\src\conf.dispatcher.d\cache\rules.any, and I have observed that images in the current Publish external environment indeed have "Cache-Control: private."

Where should I begin to address this performance issue and where can I look to identify the source of the problem?

Here's the email content:

Background:

While reviewing the logs from your Production environment, we noticed that some of the calls requesting assets are currently configured to use "private" in the Cache Control, which prevents these specific requests from being cached.

Recommendation:

We recommend adjusting the response_cache_control for the resources you want to cache by removing the "private" directive.

Including this value in the Cache Control header prevents the specified resource from being cached.