If you're still reporting on open rate as your headline deliverability metric, you're optimizing against a number that no longer reflects reality. Apple Mail Privacy Protection (MPP) prefetches images for the majority of Apple Mail users, inflating opens for sends that may never have actually reached the primary inbox.
The result: dashboards trend up while revenue per recipient quietly trends down. Worse — the engagement signal you're feeding back into your ESP's send-time and segmentation logic is contaminated.
The metrics that still tell the truth
Click-to-delivered ratio. Clicks are intentional and largely immune to MPP inflation. Track CTR against delivered (not opens) as your primary engagement signal.
Inbox placement rate from seed testing. Use tools like GlockApps or Inbox Monster to monitor placement across Gmail, Outlook, Yahoo, and Apple in real time.
Spam complaint rate. Anything north of 0.10% in Gmail Postmaster is a reputational alarm bell — act, don't watch.
Revenue per recipient. The only metric that matters at the business level. If RPR is dropping while opens climb, you're losing placement.
What to do this week
Rebuild your engagement segments using clicks + site visits + purchases — never opens alone. Then re-warm your dormant cohort behind a separate sending identity so reputation damage stays contained.
Want this audited on your program?
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