Apple MPP (Mail Privacy Protection)

Apple Mail Privacy Protection (MPP), introduced in iOS 15, allows Apple Mail users to prevent senders from knowing when they've opened an email. It does this by routing email pixels through Apple's proxy servers and pre-fetching them — making it appear that every email was opened by every Apple Mail user, regardless of whether they actually opened it. This inflates open rate metrics significantly for publishers whose audience uses Apple Mail. For ad serving, MPP creates a challenge: a pixel fired by Apple's proxy doesn't represent a genuine human open. MailAdx handles MPP in two ways: (1) it detects Apple proxy signatures in open-time requests and labels them as 'MPP-triggered' in delivery reporting, and (2) it separates MPP impressions from genuine human opens in publisher analytics, giving publishers accurate open-rate data.