Ok, that sounds a bit cryptic. What we mean is that you can't always rely on the reported number of people who have opened your email as being the actual number that did. That doesn't mean you shouldn't look at it - we do because it allows you to compare one email with another - but there are several reasons why the actual figure won't be dead on the mark:
The next question is whether they have read the contents of your email but that is a topic for another time. In the meantime, talk to us for more information about email marketing.