"Return Receipts" feature offered in email clients almost never works. The majority of all email software and users in the world do not support these kinds of Return Receipts.
Wouldn't it be nice to know when your emails gets received and where? there exist many services which lets you track your messages, these services can also be used to provide certified "Email Read Receipt", You can also retract your emails in case you changed your mind. You can also send self-destruct emails which expire after a certain time period, or if your recipient tries to copy, print or forward them.
You even don't need to download or install anything, just append the email tracking service provider's domain to end of receivers email id and it will be tracked automatically.
These services offer features like:
- Self Destructing Emails
- Stop printing and copying of email
- Date and time of message opening
- Location of recipient (IP based on ISP city /town)
- Map of location
- Apparent email address of opening (if available)
- Referrer details (ie; if accessed via web mail etc)
- URL clicks
- How long the email was read for
- How many times your email was opened
- If your email was forwarded, or opened on a different computer
Ever wanted to see when you email was opened, at what location and which links were clicked ? There are quite a few services which offer this 
