# Open rate: Definition and How It Works

Source: https://wraps.dev/glossary/open-rate

Metricsemail open rateopen tracking

Open rate is the share of delivered messages whose tracking pixel fired — historically the headline engagement metric, but heavily inflated since 2021 by Apple's Mail Privacy Protection pre-fetching images regardless of whether a message was actually opened.

## How the measurement actually works

Open tracking works by embedding a tiny, uniquely-URLed tracking pixel in the message body — when the recipient's mail client renders images and loads that pixel, the request to fetch it is logged as an open. That means the metric doesn't measure "did a human read this," it measures "did something load this specific image," which used to be a reasonable enough proxy before a major mailbox client changed how it loads images.

## Apple's Mail Privacy Protection broke the proxy

Since 2021, Apple Mail (on by default for Mail Privacy Protection-enabled accounts) pre-fetches and proxies all images in a message at delivery time, regardless of whether the recipient ever opens it, specifically to prevent senders from using pixel tracking to learn when and whether a message was read. For any list with a meaningful share of Apple Mail users — which is most consumer lists — a substantial fraction of "opens" now reflect this proxy pre-fetch, not a human actually opening the message.

## The inflation isn't a fixed, predictable percentage

How much a given list's open rate is inflated depends on what fraction of recipients use an MPP-enabled Apple Mail client, which varies list by list and audience by audience — there's no single correction factor to subtract that works generically. This makes open rate not just less accurate than it used to be, but less consistently comparable across different lists and different time periods than it used to be, too.

## Click-through rate is the more trustworthy signal now

A click still requires an actual human to interact with a specific link inside the message, which Apple's pre-fetch proxy does not simulate — click-through rate, and click-to-open rate calculated against it, are considerably more resistant to this specific distortion and are the metrics worth weighting more heavily now that a raw open count can no longer be trusted at face value.

## Why it matters

Making sending decisions off open rate alone — deciding a subject line "worked" because opens went up, or judging list health by a rising open trend — risks optimizing for something that increasingly measures Apple's own infrastructure behavior rather than recipient engagement, which is exactly the kind of quiet metric failure that doesn't announce itself until the underlying decisions it drove stop making sense.

## Common questions

### Why did my open rate suddenly jump without any change to my campaigns?

Apple's Mail Privacy Protection, on by default for many Apple Mail users, pre-fetches images at delivery time regardless of whether the message is actually opened, which inflates the open-tracking pixel's fire rate independent of any real change in recipient behavior.

### Should I stop looking at open rate entirely?

Not entirely, but weight it less than click-through rate, which still requires genuine human interaction with a link and isn't simulated by Apple's image pre-fetch. Open rate is still directionally useful for very large trend shifts, just no longer a precise engagement number.

### Does open-rate inflation affect every list equally?

No. It scales with how much of a given list uses Mail Privacy Protection-enabled Apple Mail, which varies by audience — there's no single, fixed correction factor that applies the same way to every list or every campaign.