Hi.
I would like to add some points to John's answer which of course is correct.
I would not rely in read confirmation. This confirmation is based on a setting that the user must enable. Generally, in email, I believe, there are to kind of confirmations:
- Delivery receipt
- Read receipt
Neither of those is guaranteed to be returned, as many servers do not respond with a delivery receipt, and many users set their mail clients to not send a read receipt.
Andreas.