Deliverability & the inbox
Apple Mail Privacy Protection (MPP)
Also known as: Apple MPP · mail privacy protection
An iOS 15+ and macOS 12+ feature that pre-fetches tracking pixels and masks recipient IP addresses for users who opt in — inflates apparent open rates to near 100% and breaks open-based engagement metrics for Apple Mail clients, which represent 50%+ of email users.
Apple Mail Privacy Protection, released with iOS 15 in September 2021, pre-fetches tracking pixels on behalf of Mail users who opted into the feature (the default choice on first launch). This means open-rate pixels fire whether the user opened the email or not — so open rate from Apple Mail clients is effectively 100% and meaningless as an engagement signal. Open rates across the industry inflated 15-40 percentage points after MPP rollout depending on Apple Mail share. MPP also masks recipient IP addresses via proxy, which breaks geo-based send-time optimisation for Apple users. The implications are still reshaping lifecycle measurement: open rate cannot be used as a reliable engagement signal on any segment with significant Apple Mail share. Replace opens with click-based engagement scoring, reply tracking, and forwarding behaviour for scoring and suppression.