Are Email Open Rates Accurate? Why We Stopped Trusting Them

Short answer to “are email open rates accurate”: no — and not in the direction most people assume. The folk understanding is that opens under-count because some clients block images. That was true. Since 2021, the bigger distortion runs the other way: Apple Mail registers opens for messages no human read, at the scale of one of the largest mail clients in the world.

This matters operationally, not just philosophically. Teams conclude a subject line “won” an A/B test, that a list is “engaged”, or that Tuesday sends “perform better” — on a metric that a proxy server partially generates. The failure mode of an inflated metric is worse than a missing one: it manufactures confidence.

An “open” has never been directly observable. What senders actually do — Postmark documents its own mechanics openly — is embed a unique, invisible 1×1 image in each message. When a mail client downloads that image, the sender’s server logs the request and calls it an open.

Every weakness of the metric follows from that proxy: clients that block remote images produce reads with no recorded open; preview panes can trigger downloads without a real read; corporate security gateways pre-fetch content while scanning; and cached images can swallow repeat opens. Open tracking was always an estimate wearing a percentage sign.

What changed in 2021 is that the noise stopped being random. One vendor began systematically firing everyone’s pixels.

Mail Privacy Protection (MPP), introduced with iOS 15 and enabled by a prompt most users accept, does two things per Apple’s documentation: it hides the recipient’s IP address, and it downloads remote content privately in the background when the message arrives — not when the user views it. Tracking pixels are remote content.

The scale is what makes this fatal for the metric. Postmark’s analysis puts it bluntly: you could see effectively a 100% open rate for your Apple Mail recipients whether or not they open your messages — and the larger the Apple Mail share of your audience, the more your aggregate open rate inflates. Gmail adds its own wrinkle by serving images through its proxy servers, which further blurs device and location data even when timing is roughly preserved.

We did not delete the metric — we demoted it. An open rate still carries two honest signals, both relative, neither about engagement:

• A deliverability canary. MPP inflation is roughly constant for a stable audience — so if opens on the same list suddenly collapse from one week to the next, something real changed, and spam-folder placement is the first suspect. The absolute number is meaningless; the delta is informative.
• A gross delivery sanity check. Near-zero opens on a decent-sized send almost always means a routing or reputation problem, not universally ignored copy.

What opens can no longer support: engagement scoring (an MPP prefetch is not interest), “opened but did not reply” segmentation for aggressive re-targeting, and subject-line A/B tests judged on opens — a test partially scored by Apple’s servers. This is why our own subject-line A/B system picks winners on downstream reply rates per variant, never opens.

The replacement stack is the set of events a proxy server cannot fake:

This is the hierarchy BusinessMCP’s campaign stats are built around: the console reports prospects → contacted → replied → meetings → pipeline, subject A/B winners are chosen on reply rate, and the sending-health panel watches the bounce and complaint bands that Google and Yahoo actually enforce — the full context is in our deliverability guide.

One honest limitation: reply-based metrics are slower and smaller-N than opens, so conclusions need more volume before they are real. We would rather wait for significance than optimize a fiction — the same reason the industry benchmarks inside our platform only surface k-anonymized numbers once segments cross a minimum sample size, and why our send-time guide refuses to invent a magic hour. If your sequences are underperforming, the fix is almost never metric tuning — it is the follow-up structure and the targeting.