Open Rate (Definition)
When sending an HTML email, it's possible to track the number of times an image has been displayed in an email. While not a perfect proxy, when that image is displayed it can be assumed that a human or a machine on the receiving end of that email opened it in some manner. This measure is what has become known as an email "open rate".
Open rates can not be tracked when sending plain text emails, since those messages do not contain an image to be displayed.
These days, there are many types of automation that also impact open rates and can lead to measured rates that are higher than the real number of humans that might have engaged with your emails.
- Apple iOS 15 in the fall of 2021 released features that automatically download and display images in email messages with those devices are connected to wifi and plugged in. Read more about Apple iOS 15 Mail Privacy Protection (MPP) open rate impacts.