If you want to track whether an email has been opened, you can add a tracking image to your email.
The metrics derived from tracking emails should not be regarded as 100% reliable. In particular, the lack of any tracking feedback from a particular contact doesn't mean they haven't received or opened the email. It probably means that the tracking mechanism has been blocked by their email client.
To do this, add it to your email text when creating the email like so:
When your email has been sent out, you can review who has definitely received the email by looking at the "Track Emails" tab and choosing "Build Report"
