title: MS Outlook is removing hidden text in reply email
body: <p>We have Ruby script that fetch and parse reply emails from our clients and putting them on appropriate client object in application. </p>
  
  <p>For that purpose we send email to client with specific "hidden" code/id inside 1x1 pixel img tag (in similar way tracking pixel technology works) when clients reply to email, they quote our original email with code/id inside. And when we get client reply we can detect that hidden code from img tag, and process it accordingly. This works fine except when clients are replying from Outlook 2013.</p>
  
  <p>Outlook 2013 removes image data containing code/id, and put something like "Image removed by sender." so we cannot detect see code/id anymore.
  Also tried, making a image from base64 and even encoding code/id inside base64 image, but we got same result.</p>
  
  <p>We tried different solutions, like making custom tags with class name contain code/id. Those custom tags are removed too, and replaced with something like &lt; o:p >&lt; /o:p ></p>
  
  <p>We tried to put code/id inside invisible div, in inline css and various css tricks, and in this case Outlook just removes invisibility of div, and code/id is visible in email content.</p>
  
  <p>There is a option that code/id is visible text inside body or subject, but we would like that this code/id be stays invisible to the clients.</p>
  
  <p>It seems like its almost impossible to pass some hidden data trough reply email from MS Outlook.</p>
  
  <p>Is there any way that we can pass this code/id trough reply email from outlook, without outlook removing it or making it visible?</p>
  
  <p>Thank you.</p>