Open rates are as accurate as it’s possible to make them, which will be easier to understand once you know how they are tracked.
A very tiny image is automatically placed in the bottom, left corner of every email sent out through our mailing system. This image is stored online and is uniquely linked to the email (and therefore email address) in which it appears. (By the way, it’s too tiny to see.)
When a reader opens your email, most of the time the images (including the tiny tracking one) download automatically. As the tracking image downloads, the mailing system records which email address downloaded it. This is counted as an ‘open’ and it should happen every time the email is opened.
The only time this open isn’t recorded is if the image isn’t allowed to download. Some people choose not to download images, which skews the open rate stats. Unfortunately this remains the user’s choice and we can’t force them to download images. Luckily Gmail has now made downloading images the default setting (it wasn’t always like this).
All this is why open rates aren’t a perfect means to track an email. Often checking click throughs gives a better indication of how people are interacting with your newsletter. However, click throughs are only a good indicator if your email is set up to support this. More on this next week!
Note: All mailing systems track open rates in the same way, so ALL OF THEM have this same capacity for inaccurate results.