This service brings nothing more to the email usability than the usual read receipts do. But has massive limitations that read receipts dont.

This only works for people who are reading their emails in HTML format and allowing external images to load in their email client ( in other words - brain dead users with brain dead email client s/w )

The 'trick' used is that they drop an image into the html of the email that links to an image hosted on their server ( normally 1px by 1 px - so most people will not notice it ). This is also the trick used by Spammers to verify email accounts.... Most email clients these days will now not allow you to load an image or link to any website from an email message ( or have an option to this effect anyway ).

So if you really want to track how / where you email is and if it was read, use the Read-receipt-notification option, it works in any and every kind of email and on any platform / OS.

Looks like you just got scammed for $50 :)