Originally Posted by
jurupa 
AgentWinter - First off you can with certain e-mail clients make it so you can know when they received the e-mail and read it.
That's realllly hit or miss, the other person on the other end has to be using a email client that supports read receipts, and even then the other person can decline to send a read receipt, so if you do get one it's because they chose to let you know they read it.