How email open tracking works
Email open tracking sounds like magic. It isn't — and knowing how it works tells you how far to trust it.
The invisible picture
When you send a tracked email, the tracker adds a tiny, invisible picture to it. Each email gets its own picture address. When the reader's email app shows the email, it downloads the picture from the tracker's server — and the server writes down: this email was opened, at this time.
What the server can see
From that one download the server sees the time and, often, the network and kind of device. Gmail is different: it downloads pictures through Google's own image proxy, so for Gmail readers a tracker sees that and when the email was opened, but usually not the place or device.
When a picture loads without a person
- Your own reading. Looking at your Sent copy loads the picture too. Glimpse recognises your own devices and your Sent copy and leaves those out.
- Preloading. Gmail on a phone can load several emails ahead of time. When several emails to the same person load within the same few seconds, Glimpse counts the newest one and marks the others “Maybe – preloaded”.
- Spam scanners. Some companies check every incoming email with a scanner that loads pictures. Glimpse marks these “Maybe”.
- Apple Mail Privacy Protection. Apple Mail can load every picture as soon as an email arrives, read or not. Glimpse shows “arrived at Apple – can't know if read” and doesn't count it as read.
When a real read doesn't show
If the reader's email app blocks pictures — Outlook often does until the reader clicks “Download pictures” — a real read may not show at all. Plain-text email apps never load pictures.
So how accurate is it?
Popular trackers publish that an open is the recipient reading the email in around 95% of cases. That is a general estimate, not a measurement of any one tracker. Glimpse's job is to remove the cases it can recognise — and to label the rest honestly instead of guessing. Treat an open as a strong signal, not proof.
Is it private?
Glimpse keeps the subject, the recipients and the send time of the emails you track — never the text. It never sells data, shows no ads, and doesn't use your email to train AI. See our privacy policy.