How does MPP (Mail Privacy Protection) affect tracking?

Mail Privacy Protection (MPP), introduced by Apple in iOS 15/macOS Monterey (2021), significantly impacts email tracking.

• What MPP does:
• Prefetches all remote content (including tracking pixels) regardless of whether the user actually opens the email
• Routes image requests through Apple's proxy servers, hiding the recipient's IP address and location
• Caches content, so subsequent views don't trigger new requests
• Impact on open tracking:
• Emails to MPP users always appear "opened" even when deleted unread
• Open rates inflate dramatically (often 20-40% higher)
• Open timestamps don't reflect actual reading time
• You can't distinguish real opens from prefetched ones
• Impact on location/device tracking:
• IP-based geolocation fails (you see Apple's proxy IPs)
• Device/client detection becomes unreliable
• Send-time optimization based on opens breaks for MPP users
• Adaptation strategies:
• Shift focus from opens to clicks (unaffected by MPP)
• Segment MPP vs non-MPP users for cleaner metrics (some ESPs detect this)
• Use open rates as ceiling estimates rather than engagement measures
• Collect explicit preferences for timing and interests
• The lighthouse still flashes, but you can't tell who's actually watching.