Open tracking
Open tracking counts opens by putting a tiny invisible image in the message and watching for it to load. It is the weakest number in email. Many clients block images, and others fetch them through a proxy before anyone has read a word, so an open can be recorded that never happened and a real read can go unseen. Treat it as a trend.
At a glance
- Category
- Tracking
- Mechanism
- A one-pixel image whose request is recorded
- Undercounts when
- A client blocks remote images by default
- Overcounts when
- A privacy proxy prefetches images on arrival
- Best used as
- A relative trend, never an absolute count
How it works
A transparent image is added to the HTML part with a URL carrying an identifier for that message. If the reader's client loads remote images, the request reaches the tracking host and an open is recorded with the time and whatever the client sent as its user agent. If images are blocked, nothing is recorded even though the message was read. If a privacy proxy fetches images when the message arrives, an open is recorded even though nobody has looked at it.
Why it matters
Open rate is the most quoted and least reliable number in email reporting, and treating it as a measurement rather than a signal leads to bad decisions: pruning engaged readers whose client blocks images, or believing a campaign landed well because a proxy touched every pixel. Used as a relative trend between comparable sends it still carries information. Used as an absolute, or compared between audiences on different clients, it is close to meaningless.
Example
Two campaigns go to the same segment a week apart. The first shows a forty per cent open rate, the second twenty-five. The absolute values are not trustworthy, but the fall is, because the audience and their clients did not change between the two sends. The team looks at the subject line and the send time rather than concluding that half the list stopped reading their mail.
Common mistakes
- 01Treating an open as a read, when a proxy may have fetched the image before the message was ever displayed.
- 02Removing contacts who have never opened, which deletes real readers whose client blocks images by default.
- 03Comparing open rates between audiences on different clients, where the measurement itself differs more than the behaviour.
- 04Reporting an open rate to colleagues without saying what it does and does not count, which turns a weak signal into a decision nobody should have made.
In Rasket
Open tracking is per domain and off by default, capped per message, and the user agent is recorded exactly as it arrives so you can judge the proxies yourself. Tracking
Related terms
Frequently asked questions
Is open tracking worth enabling at all?
As a relative trend between similar sends, yes. As a count of people who read your mail, no, and reporting it that way tends to mislead whoever reads the dashboard.
Why are opens higher than clicks by so much?
Partly genuine behaviour, and partly because privacy proxies fetch images on arrival. Clicks require deliberate action, which is why they are the more trustworthy of the two.
Should transactional mail be open tracked?
Usually not. The number tells you nothing you can act on, and the pixel is one more remote resource in a message people expect to be plain and obviously legitimate.
Last updated 16 September 2026.
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