title: Trying to collect email analytics
body: <p>I've written an email application in PHP that handles very large mailing lists. Is there a way to find out what emails are opened and by who? Any solution will do as long as it can tell me if the user has actually received and opened the email. I do not want to use email receipts either as it may put off recipients.</p>
  
  <p>If it's relevant, I'm using the codeIgniter framework.</p>