title: How long does gmail cache images?
body: <p>Programmers who generate email know that Gmail does not display images directly from the source defined in the email message HTML; a Google proxy server requests the image from the source and caches it, and Gmail displays the image from the cache.</p>
  
  <p>For how long does Google keep the cached version of the image? In other words, how much time must transpire before Google's proxy server must request the image from the source again?</p>
  
  <p>I've searched for the answer to this on the web and come up with no answer.</p>