R. McCarty said:
You're speaking of a "Return Receipt". It depends on which email
client you are using to send the message. For Outlook Express you can
setup and control Return Receipts from Tools, Options, Receipts (TAB).
But even if you send a message "Return Receipt Requested," if you don't get
a return receipt, there's no guarantee that it wasn't opened. First, not all
E-mail clients send receipts. Second, even if the recipient is using an
E-mail client which support sending receipts, he may have turned off the
feature. So it's not a generally useful feature, and the real answer to
Elizabeth's question is that she can't do this reliably.
As a matter of fact, I recommend that everybody turn off the feature if he
has it. I keep it off, because I don't want spammers to get notification
that the address they sent mail to is legitimate.