Open rate used to be the first number anyone checked on a campaign. Three changes, in 2013, 2021 and around 2023, moved the loading of images away from the reader and onto proxies, privacy features and scanners. Below: how the pixel works, who loads it today, what it costs a cold email, and what to measure instead.
What is a tracking pixel?
A tracking pixel is a one-by-one image, usually transparent, with a unique address for each recipient. The image is not attached to the email; it sits on the sender's server. When a mail client displays the message and fetches the image, the server logs the request against that recipient and the sending tool counts it as an open.
The method has one built-in assumption: that the image is fetched when, and only when, a person looks at the message. Every problem with open tracking comes from that assumption no longer holding.
How does open tracking work, and who loads the pixel today?
Open tracking still works as designed; what changed is who loads the image. Three steps moved it away from the reader.
| Year | Change | Who loads the pixel |
|---|---|---|
| 2013 | Gmail starts serving images through its own proxy servers (Gmail blog) | Google's proxy, on the reader's behalf; the sender no longer sees the reader's IP address |
| 2021 | Apple launches Mail Privacy Protection (Apple Newsroom) | Apple Mail, in the background, whether or not the message is read |
| Around 2023 | Security scanners and mail clients prefetch messages and images before delivery | Scanners and gateways, before any person sees the email |
Years are when each change started; adoption spread over the following years.
The Apple change alone was large. Apple's privacy notice says Mail downloads remote content in the background by default, regardless of how the user interacts with the message. Litmus, tracking 1.3 billion opens in July 2022, reported Apple Mail at 57.4 % of opens and Mail Privacy Protection at 52.7 % of Apple opens. On top of that, security gateways open and scan mail before delivery, and Spamhaus notes that the same scanning makes clicks a weak metric too. The result is that a recorded open no longer reliably means a person read anything.
The changes are documented by the mail providers. The Gmail blog announced in December 2013 that images would be shown automatically through Google's own proxy servers. Apple's 2021 announcement describes Mail Privacy Protection as stopping senders from learning whether an email was opened and hiding the reader's IP address, and Apple's privacy notice confirms that Mail loads remote content in the background. Litmus measured the effect on 1.3 billion opens in 2022.
What does a pixel cost a cold email?
It costs deliverability. A tracking pixel is a remote image, and images are among the strongest signals a filter uses to separate bulk or phishing mail from a personal message. Leadspicker's guidance is that the pixel carries the same deliverability cost as any other image, and adds a remote load that ordinary personal email does not have, which is itself a flag.
A cold email from an unknown sender has no reputation to spend. Adding an image to measure something that no longer measures people is the worst trade available: a real cost to inbox placement in exchange for a number you cannot act on.
Why is open tracking off by default here?
Leadspicker has open tracking off by default, deliberately, and recommends leaving it off. Its reasoning: until around 2023 open rates were roughly accurate and could steer a campaign; since then, opens are mostly bots, and there is no reliable way to separate a scanner's open from a person's.
So the default reflects both halves of the problem. The pixel lowers the chance the message reaches the inbox, and when it does, the open it records is mostly a machine. No external study gives the exact share of machine opens; the direction is clear, the precise number is not.
What should you track instead?
Track what a scanner cannot fake. A reply means a person read the message and decided to answer.
- Reply rate: the main health metric for a cold campaign, per sequence and per step.
- Positive reply rate: replies that show interest, separated from out-of-office messages and refusals.
- Meetings booked: the outcome the campaign exists for.
- Bounce rate: a direct measure of list quality, available without any pixel.
- Complaints and unsubscribes: the early warning that targeting or volume is wrong.
If you need a sign that a message was seen before a reply arrives, read the replies themselves: an answer to step one says more than a thousand recorded opens.
Leadspicker ships with open tracking off by default because, since around 2023, most recorded opens come from scanners, and the pixel is an image with a deliverability cost.
Frequently asked questions
Why are open rates unreliable since 2023?
Because images are now loaded by machines: Gmail's image proxy, Apple Mail Privacy Protection, which fetches content in the background, and security scanners that open mail before delivery. A recorded open no longer reliably means a person read the message.
Does a tracking pixel hurt deliverability?
It can. The pixel is a remote image, and images are a strong signal filters use to flag bulk or phishing mail. For a cold sender without reputation, that is a real cost for a number that no longer measures people.
What should I track instead of opens?
Reply rate first, then positive replies, meetings booked, bounce rate and complaints. None of these can be produced by a scanner, and each points to a specific fix.
- Apple Newsroom, Apple advances its privacy leadership with iOS 15 (2021)
- Apple Legal, Mail Privacy Protection and Privacy
- Gmail Blog, Images Now Showing (2013)
- Litmus, Email Client Market Share, July 2022
- Spamhaus, Unravelling the myths of spamtraps clicking links (2023)
- GTM playbook for 2026 by Leadspicker, chapters: Why open tracking is off by default
