Email tracking / Read receipts with JMail

[zxon]

I want to be able to track when recipients have opened an email that I have sent to them using JMail. I've searched the internet for a solution and so far cannot find one. I've found these two solutions but neither will work:

• The JMail.ReturnRec eipt property
  I set this to true but receive no receipt, not even a delivery receipt. When I enable logging and print the log, it shows that a receipt was sent out so I can only assume this is a delivery receipt property and not a read receipt one.
• Adding a 1x1 pixel tracking image to the email
  This would work in theory but most email clients (Outlook, Gmail, Hotmail etc) block images by default.

Any advice would be welcome. Thanks.

[zxon]

Can anyone point me in the right direction for this please?