Understanding the email open rate

The email open rate which we show in interests.me is an "at least" number. So if the open rate is shown as 50%, it means that "AT LEAST 50% of subscribers have opened the email".

It is possible for recipients to open an email only once it has been downloaded to their email provider, and when they are off-line or when there is not a good internet connection. When this happens, our system is not "alerted" that the email has been opened and so our system cannot record it.