Are Email Open Rates Accurate? Apple Mail Privacy and the Measurement Problem

No. Open rates have been a distorted metric since 2021, when Apple's Mail Privacy Protection (MPP) started pre-loading tracking pixels for Apple Mail users — registering an "open" whether or not the email was ever read. Gmail's image proxy adds further noise. Opens remain useful as a deliverability signal, but as an engagement metric they overcount; replies are the number that can't lie.

How open tracking works — and how it broke

An "open" is a 1×1 transparent image (the tracking pixel) loading from the sender's server. That mechanism assumes images load when, and only when, a human views the email. Two providers broke that assumption:

• Apple Mail Privacy Protection (iOS 15+, 2021): Apple Mail fetches remote content — including tracking pixels — through Apple's proxies in advance, regardless of whether the user reads the message. Every MPP-protected recipient can register as an "open." With Apple Mail's large share of B2C and meaningful share of B2B reading, this alone inflates open rates substantially.
• Gmail's image proxy: Google has long cached images through its own servers, which masks the recipient's device and location and can decouple pixel loads from actual reads in prefetch scenarios.

The result: a reported 60% open rate might be 40% humans and 20% robots — and you cannot tell which from the dashboard.

What opens are still good for

Direction, not truth. Because the inflation sources are roughly constant within your audience, changes in open rate still carry signal: a sudden drop usually means a deliverability problem, not a measurement artifact — the diagnostic sequence in why your open rate is dropping still applies. Cross-campaign comparisons on the same list remain informative. Absolute numbers ("we get 70% opens!") are marketing fiction.

What to measure instead

• Reply rate — a reply requires a human. It's the cold email KPI that survived the privacy era intact; benchmarks in what is a good reply rate.
• Positive reply rate — replies minus the "remove me" responses; the number that actually predicts pipeline.
• Bounce rate and spam-complaint rate — the health metrics mailbox providers themselves judge you on.
• Meetings booked per 100 sends — the business metric the whole funnel exists for.

In Sales.co platform data (5M+ cold emails, 2025–2026), the campaigns that look best on opens and the campaigns that book the most meetings are frequently different campaigns — subject-line bait inflates the first and quietly suppresses the second. Optimizing for the wrong metric isn't neutral; it's negative.

There's also a delivery-side reason to rethink the pixel itself — covered in do tracking pixels hurt deliverability. Platforms like Sales.co report reply-centric analytics by default, so campaign decisions ride on numbers a privacy proxy can't fake.