title: Prevent Gmail from caching images in newsletter
body: <p>Since December Gmail is caching all images.</p>
  
  <p>Now dynamic images e.g. countdowns won't work properly. Once the image is cached the timer will show the time as the image was cached by google and won't update itself.</p>
  
  <p>I've found a fix (and for those who want to help a further explanation): <a href="http://blog.movableink.com/real-time-content-and-re-open-tracking-return-to-gmail/" rel="noreferrer">http://blog.movableink.com/real-time-content-and-re-open-tracking-return-to-gmail/</a></p>
  
  <p>Now my problem: What do I have to do?</p>
  
  <p>I tried adding "no-cache" and "max-age=0" to my header but Gmail is still caching it.</p>
  
  <p>Here is my full header</p>
  
  <pre><code>header( 'Last-Modified: ' . gmdate( 'D, d M Y H:i:s' ) . ' GMT' );
  header( 'Cache-Control: no-store, no-cache, must-revalidate, max-age=0' );
  header( 'Cache-Control: post-check=0, pre-check=0', false );
  header( 'Pragma: no-cache' ); 
  </code></pre>
  
  <p>I've also tried using only "no-cache" and "max-age" and other combinations as well, nothing seems to work.</p>
  
  <p>Any suggestions?</p>