What is an ESP (Email Service Provider)?

Apple Mail Privacy Protection is a feature introduced in iOS 15, iPadOS 15, and macOS Monterey in September 2021 that prevents email senders from tracking when recipients open their emails. When enabled, MPP routes email content through Apple proxy servers that pre-fetch images and other remote content, including tracking pixels, regardless of whether the recipient actually views the email. This makes it impossible for senders to reliably determine if Apple Mail users opened their messages.

MPP affects email marketing measurement significantly because open tracking relies on tiny invisible images that load when an email is viewed. With MPP, these pixels load automatically when the email arrives on Apple's servers, registering as an "open" even if the recipient never looks at the message. For senders, this means inflated open rates, inaccurate engagement data, and broken automations that trigger based on opens.

The feature is opt-in for users but presented prominently during Mail app setup, leading to high adoption rates among Apple Mail users. Since Apple Mail represents a substantial portion of email opens across consumer and business audiences, MPP fundamentally changed how marketers measure email performance. MPP marked a shift toward greater email privacy that continues reshaping industry measurement practices.