Did they read it is a service where your can track your mails. You need to register to this site, and add .didtheyreadit.com , at the end of the recipients email address, Don’t fear, because the updated mail address wont be visible to your friend.
This will not only track the mail, it will tell you the physical area as where the mail was opened, when it was opened, and for how long it was opened.
If you are using Outlook Express, then there is a tool provided, which when installed, can be used to track mails. This service is not free, but gives you an option to try the service, with 10 mails to track. You too can try.
Did they read .. The Best Email Tracking Software Sends You Email Message Read Receipts
For more .. Tech Check
Track Emails You Send .. 
Linear Mode
