Email open tracking works by embedding a tiny, invisible image, a tracking pixel, in an email. The recipient's mail client loads that image. The sender's server logs an "open" the moment it does. That tracking pixel and the HTML it requires carry a real deliverability cost for cold email specifically, and the open data it produces is no longer reliable enough to justify it.
This page covers how open tracking and tracking pixels work, why Apple Mail Privacy Protection broke open rate as a metric, and what a tracking pixel and a custom tracking domain cost a cold email campaign in deliverability. It also covers what to measure instead of opens. It builds on our cold email benchmarks guide, which covers open and reply rate benchmarks in more depth than this page's narrower focus on tracking itself.
How does email open tracking work in cold email?
Email open tracking works by inserting a 1x1 pixel, an image so small it is invisible, into the HTML version of an email, with a unique tracking link as its source URL. When the recipient's email client fetches that image to display the message, it sends a request to the sender's server. That request is logged as an open.
The pixel only works in the HTML version of an email, because a plain text email has no images to load and nothing to trigger the request. That is the core mechanical fact behind every open-tracking tool: without HTML, there is no pixel, and without a pixel, there is no logged open. A tracking link added to any clickable text in the body works the same way for click tracking, routed through a tracking domain rather than the destination URL directly.
Why are cold email open rates unreliable since Apple Mail Privacy Protection?
Cold email open rates became unreliable once Apple Mail Privacy Protection started pre-loading every image in every email in the background, whether or not the recipient ever opens the message. That background load registers as an "open" on the sender's side exactly the same way a real open does, so a meaningful share of logged opens are not real opens at all.
Apple's own description of the feature states that Protect Mail Activity "downloads remote content in the background by default, regardless of whether you engage with the email." It routes that download through two separate relays run by different entities. No single party can trace the activity back to one person. The feature is on by default for anyone who has not explicitly turned it off, and once chosen, that setting syncs across every device tied to the same Apple ID.
Our cold email benchmarks guide covers this mechanism in more depth and what it does to published open rate figures across the industry. The practical result for anyone running cold email is that an open rate report now mixes real opens with background downloads, with no way to separate the two from the sender's side. That makes open rate a weak signal to optimize toward no matter which tool is reporting it.
What does open tracking cost cold email in deliverability?
Open tracking costs cold email deliverability in two ways. The tracking pixel requires an HTML email, and HTML carries more spam signals than plain text does. A link-tracking domain also adds a second domain's reputation into every message a recipient's mail server has to evaluate.
- The HTML requirement. A tracking pixel only works inside an HTML email, which means a sender who wants open data has to send HTML rather than plain text. Spam filters weigh HTML-heavy formatting, embedded images and a mismatch between a message's apparent simplicity and its underlying markup, all of which a plain text cold email avoids entirely.
- The tracking domain. A tracking pixel and tracked links are usually served from a separate domain controlled by the sending tool, not the sender's own sending domain. That tracking domain carries its own reputation, built from every other customer using the same tool, and a receiving mail server evaluates it alongside the sending domain itself.
Neither cost is really about the pixel's size or the request it triggers. It is about what wrapping a plain message in HTML and routing it through a third-party domain signals to a spam filter that is already suspicious of unsolicited mail by default.
What is a custom tracking domain, and does it fix the cold email problem?
A custom tracking domain is a subdomain you control, pointed at the tracking tool's infrastructure, used in place of the tool's own shared tracking domain for links and pixels. It replaces one risk with a smaller one. A custom tracking domain carries only your own sending reputation rather than a shared one built from every other customer of the same tool. It still adds HTML and a redirect layer that a plain text email does not need.
Setting one up correctly needs its own DNS record pointed at the tracking provider, kept separate from your actual sending domain's SPF, DKIM and DMARC setup covered in our SPF, DKIM and DMARC guide. A custom tracking domain is a meaningful improvement over a shared one for anyone sending HTML regardless. It does not remove the underlying cost of sending HTML and tracked links on a cold list in the first place.
What should you measure instead of open rate in cold email?
Measure replies, positive replies and meetings booked instead of open rate, because all three require the recipient to actually engage, which a background pixel load cannot fake. Our cold email benchmarks guide covers published reply rate figures in full, including the oft-cited average around 3.43%, a steadier number than open rate because nothing short of a genuine human response can produce it.
| Metric | What triggers it | Reliable for cold email? |
|---|---|---|
| Open rate | Image load, real or automated | No, inflated by Apple Mail Privacy Protection and similar background loading |
| Click rate | A link click | Partially; also loaded by some automated scanners and preview tools |
| Reply rate | A written response | Yes, requires genuine engagement |
| Positive reply rate | A response expressing interest | Yes, the number that actually predicts pipeline |
| Meetings booked | A scheduled call | Yes, the clearest outcome metric of all |
A campaign that tracks only replies and meetings loses nothing meaningful compared to one that also tracks opens, since opens were never telling the sender anything an inbox full of actual replies does not already show more reliably.
Does Pipefire use open tracking on cold email?
No. Pipefire sends plain text cold email with no HTML part and no open tracking or tracking pixel, on purpose. There is no open rate in Pipefire's reports, because we do not measure one, and plain text avoids both the HTML deliverability cost and the tracking domain reputation question covered above entirely.
Replies are what we track and sort instead: every incoming reply is categorized automatically, warm ones are flagged, and a person approves every answer before it sends. If a campaign's performance needs to be read from somewhere, reply activity is the signal we build toward, not a pixel load that Apple Mail Privacy Protection would make meaningless anyway. See what Pipefire includes for the full picture.
Email open tracking cold email FAQ
How does an email tracking pixel work in cold email?
A tracking pixel is a tiny, invisible image embedded in an HTML email with a unique URL. When the recipient's mail client loads that image, it sends a request to the sender's server, which logs the request as an open.
Why did Apple Mail Privacy Protection break open tracking for cold email?
Apple's Mail Privacy Protection pre-loads every image in an email in the background by default, whether or not the recipient opens it, which registers as an open on the sender's side regardless of real engagement. Apple's own description confirms the feature downloads remote content "regardless of whether you engage with the email."
Does turning off open tracking hurt cold email performance?
No. Open rate was never a reliable signal, especially after Apple Mail Privacy Protection, so removing a tracking pixel loses a noisy, partly-fake metric while avoiding the HTML and tracking domain costs that came with collecting it.
What is a custom tracking domain used for in cold email?
A custom tracking domain routes tracked links and pixels through a subdomain you control rather than the tracking tool's shared domain. That keeps its reputation separate from other customers of the same tool. It still does not remove the underlying cost of sending HTML on a cold list in the first place.
What should I track in cold email instead of open rate?
Track replies, positive replies and meetings booked. All three require genuine engagement from the recipient, unlike an open, which a background image load can trigger without anyone reading the message.