What is Open Rate?

Open rate is a core email marketing metric: the percentage of delivered messages that were opened by recipients. It is calculated by dividing unique opens by the number of emails successfully delivered, and it has long served as a first-glance indicator of how compelling your subject line and sender name are.

Opens are traditionally tracked with a tiny invisible image, the tracking pixel, embedded in the email. When a recipient's client loads that image, the request registers an open. This method works well in aggregate but has always been imperfect, since it only counts opens where images actually load.

That imperfection became a major limitation with Apple Mail Privacy Protection, which pre-loads tracking pixels for all users regardless of whether they truly opened the message. This inflates open rates and makes them unreliable as an absolute measure, especially for audiences heavy on Apple Mail.

As a result, savvy senders now treat open rate as a directional, comparative signal rather than a precise truth, and lean more on downstream metrics like clicks and replies that indicate genuine engagement. Open rate still has value for A/B testing subject lines and spotting deliverability problems, but it should not be the sole measure of success.