You can use the AdditionalHeaders field to add the "Return-Receipt-To:" header. I'm not sure how many mail clients actually respect this header.
The mail client will send you an email when the message is opened.
Another option is to create a html email and include an image that will be downloaded from your server. You can add parameters to the url to identify it.
...
Another option is to create a html email and include an image that will be downloaded from your server. You can add parameters to the url to identify it.
To expand on that: It assumes that the email client (or a users configuration of it) opens the email as an HTML and not just plain-text. If plain-text, then the image flag is never downloaded. The default install for all of our clients' email systems are to open emails as plain-text only.