# Email opens are a weak metric. Measure these instead

*Published: 2026-08-24*

I still look at open rate. I just don't let it pick the winner.

In June 2021 Apple said [Mail Privacy Protection](https://www.apple.com/newsroom/2021/06/apple-advances-its-privacy-leadership-with-ios-15-ipados-15-macos-monterey-and-watchos-8/) would stop senders from using invisible pixels to learn when a person opened a message, and would mask the IP so it couldn't be tied to other activity or a location. Their [privacy write-up](https://www.apple.com/legal/privacy/data/en/mail-privacy-protection/) is more mechanical. Protect Mail Activity downloads remote content in the background when the message arrives, whether or not anyone engages with it.

If you still make list and creative decisions on opens alone, you're reacting to a prefetch, not a reader.

## Key takeaways

- [Mail Privacy Protection](https://www.apple.com/newsroom/2021/06/apple-advances-its-privacy-leadership-with-ios-15-ipados-15-macos-monterey-and-watchos-8/) prefetches remote content when the message arrives. An open is a pixel fetch, not proof someone read the mail.
- Prefer human clicks, replies, the conversion named in the brief, and complaint rate. Drop click-to-open on an MPP-heavy list.
- [Gmail](https://support.google.com/a/answer/81126) still publishes spam-rate ceilings of 0.1% and 0.3%. That number belongs next to revenue.
- On Brew, a click we believe is a real person is never labeled a bot. The other direction is allowed when the pattern is clearly automated.

## Why opens broke

[Apple's Mail Privacy Protection](https://support.apple.com/en-us/HT212559), in the Mail app on iOS 15 and later, hides the recipient's IP and **prefetches images**, including the tracking pixel most ESPs still use. The prefetch can fire whether or not anyone opened the message.

Apple does not publish the share of mail that hits MPP. You can see the effect in your own data. Unique opens step up after a list picks up more Apple Mail, and clicks stay flat. That pattern is the tell. It is not a sudden improvement in the creative.

Other clients prefetch too. The honest position is this: **an open is a hint that a client fetched a pixel.** It is not evidence that a person read the subject, let alone the body.

## What to use instead

| Signal | What it can tell you | What it cannot |
| --- | --- | --- |
| **Click, human** | Someone chose a link | Whether they finished the job on the other side |
| **Click-to-open** | Useless if opens are inflated | Do not use this ratio on an MPP-heavy list |
| **Reply** | A person wrote back | Volume will be low. Still a clean signal |
| **Conversion** | The email did the job you named | Needs the job defined in the brief, not "engagement" |
| **Unsubscribe / complaint** | The mail cost you trust | Complaints are the one Gmail will throttle you on |

[Gmail's bulk-sender page](https://support.google.com/a/answer/81126) is explicit about spam rate. Stay under **0.1%**, and treat **0.3%** as a hard ceiling. That number belongs on the same dashboard as revenue, not in a deliverability appendix.

## How we treat a click

Bots click. Prefetchers click. Some security gateways open every URL in a message.

Our rule on the Brew side is simple. **A click we believe is a real person must never be labeled a bot.** We'd rather leave a suspicious click in the human bucket than throw away a customer who used a strict corporate filter.

The reverse is allowed. Automated patterns can be dropped from "human clicks" when we are sure. That bias is deliberate. A vanity bot-rate feels good in a screenshot and lies in a report to finance.

If your ESP lets you choose the bias the other way, know that you're optimizing a chart, not a decision.

## A dashboard that survives MPP

For a campaign, I want four numbers in this order:

1. **Sends** that left the ESP, accepted, not just "queued."
2. **Human clicks**, using whatever bot filter you trust, documented.
3. **The conversion you named in the brief.** First send, purchase, booking.
4. **Complaints and unsubscribes**, as rates, not raw counts hidden on page four.

Opens can sit on row five, labeled as pixel fetches. Use them to spot a rendering problem, when opens and clicks collapse together, or a list that suddenly tilted toward Apple Mail, when opens jump and clicks do not.

## What I stopped doing

I stopped killing variants on open rate. I stopped calling a 40% open "healthy" without looking at clicks. I stopped reporting click-to-open to anyone who still thinks the denominator is people.

The email either moved the job you wrote down, or it didn't. The pixel will not tell you.

Name the job in the [brief](/blog/how-to-brief-an-email-agent) before you look at a chart. For inbox placement, use [email deliverability](/blog/email-deliverability). For the legal split that changes which headers you send, use [transactional emails](/blog/transactional-emails). To contact us about this article, write [Brew support](/support).

## How to use this page

**An email open** is a pixel fetch, which mailbox prefetch can trigger without a reader.

**A human click** is a click Brew is willing to treat as a person, not a scanner.

**Click-to-open** is a ratio with an inflated denominator after Mail Privacy Protection.

For example, a corporate preview pane can fetch every image and look like a 100% open rate.

| Move | Why it matters |
| --- | --- |
| Name the job first | Then pick the metric that proves it |
| Keep complaints on the dashboard | They are the metric mailbox providers already use |

US commercial mail still follows the [FTC CAN-SPAM guide](https://www.ftc.gov/business-guidance/resources/can-spam-act-compliance-guide-business) and [16 CFR 316.3](https://www.ecfr.gov/current/title-16/chapter-I/subchapter-C/part-316/section-316.3). Bulk sending still has to meet [Gmail's sender requirements](https://support.google.com/a/answer/81126). To contact us about this article, use the support link above.

## Frequently asked questions

### Why are email open rates unreliable?

[Apple Mail Privacy Protection](https://support.apple.com/en-us/HT212559) prefetches images, including tracking pixels, when the message arrives. Other clients prefetch too. An open means a client fetched a pixel.

### What should I measure instead of opens?

Human clicks, replies, the conversion you named in the brief, and unsubscribe or complaint rate. Opens can sit on row five, labeled as pixel fetches.

### What is click-to-open after MPP?

A ratio with an inflated denominator. Do not use it to pick a winner on a list that tilts toward Apple Mail.

### How does Brew classify clicks?

A click we believe is a real person is never labeled a bot. Automated patterns can be dropped from human clicks when we are sure. The bias is deliberate so a corporate filter does not erase a customer.