http://www.politechbot.com/p-03580.html
[How rude and annoying. From now on, I'm only going to use /usr/bin/Mail or maybe tail -100 from the mail spool... --Declan]
--- From: [deleted --DBM]
Subject: Neulevel's PostMinder tracks e-mails without recipient approval
Neulevel's PostMinder tool <http://www.postminder.biz> sends out confirmations to the sender that the recipient has read an e-mail even when the recipient has disabled Return Receipts.
If your mail reader displays HTML, it will send a message back to Neulevel to indicate that your message has been read. In addition, it displays a message "The sender of this message requests confirmation when you read it. Click here to confirm." No need to click -- it has already been confirmed.
If you dislike this, you can set your mail reader to Text-only/no HTML allowed.Eudora users can disable "Use Microsoft's viewer" (Tools/Options/Viewing Mails).