WebEngage is serving over 100 million widget requests per month

<p><pre><code> Cache-Control: private, max-age=600 </code></pre> With an explicit version number in the URL, there's little reason to have a 10 minute expiration period for a .js file. Why not save bandwidth and money (and improve performance to boot) with a more reasonable expires setting?

Use Entity Tags and Last-Modified Dates as far as possible for caching. other options may be Module mod_expires