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.