Mail Privacy Protection
Apple's feature (since iOS 15, 2021) that preemptively loads email images — inflating open rates for Apple Mail users.
Mail Privacy Protection (MPP), introduced with iOS 15 in 2021, is Apple's feature that preemptively fetches all images in incoming emails from Apple's servers before the user opens the message. The intent is privacy (the actual recipient's IP and open behavior are masked from the sender). The side effect is that open-tracking pixels fire whether or not the user actually opens the email.
For senders with Apple-heavy audiences (consumer DTC, lifestyle brands, B2B audiences using iPhones for work email), open rates have effectively become "rate at which the email arrived in any folder for an Apple Mail user." The metric is inflated and decoupled from actual engagement.
Adaptation has been gradual. Modern email programs increasingly rely on click-through rate as the primary engagement metric, since clicks are user-actuated and don't suffer MPP inflation. Some senders try to segment Apple Mail users out of open-based reporting; in practice, the cleanest fix is just to use click rate as the headline.