Open Rate

Understanding Open Rate

Open rate has been a staple email marketing metric for decades, but its reliability has decreased significantly. Email opens are tracked by embedding a tiny invisible image (tracking pixel) in the email. When the recipient's email client loads this image, it registers as an open. This method was never perfect, but it was good enough for directional measurement.

Apple's Mail Privacy Protection, introduced in iOS 15, fundamentally changed open rate accuracy. Apple now pre-loads tracking pixels for all emails received in Apple Mail, regardless of whether the user actually opens the email. Since Apple Mail accounts for roughly 50-60% of email opens in many consumer audiences, this inflates open rates significantly and makes them unreliable as an absolute metric.

Despite these limitations, open rate still has value as a relative metric. If you send two subject line variants to the same audience, the one with the higher open rate likely has the better subject line, even if the absolute numbers are inflated. Open rate trends over time also remain meaningful: if your open rate drops consistently over months, something is likely wrong with your sender reputation or audience relevance.

Smart email marketers have shifted their primary metrics from open rate to click rate, click-to-open rate, and revenue per email. These downstream metrics are not affected by pixel pre-loading because they require actual recipient interaction. Open rate remains useful for subject line testing and deliverability monitoring, but it should no longer be the primary measure of email performance.