Why you shouldn't use open rates to measure email marketing effectiveness
What's changed?
"Open Rate" is measured by inserting a tiny invisible image (called a pixel) into emails. When the image is downloaded, usually by the user opening the email, the system sending the email records this as an 'open' event.
A number of email providers have implemented changes to their devices/web apps to improve the user experience by downloading images immediately when the service receives the email to eliminate the downloading delay when opening the email.
This is a great experience for the end-user, but a negative experience for marketers as 'open rates' can no longer be considered accurate.
How should I track my campaigns in future?
Focus more on other metrics such as click-through rates, traffic to your website, click-maps, and unsubscribes.