Is there a way that you can check if someone has opened an email that you've already sent?

I know there are programs that you can download to track emails before you send them but are there any that you can use after the fact?

Is there a way that you can check if someone has opened an email that you've already sent?
No, afraid not, once you've sent it, it's gone. You have to set the read receipt before you send, and even then, often the recipient can override it.
Reply:Not 100%. Email doesn't work that way. Outlook has the option to "Request Receipt confirmation" but the user doesn't have to respond. Email is just like regular mail. The mailman can deliver it, but its up to the user to open it.