What is an email tracking pixel? How opens are tracked

How a tracking pixel works

An email can include images hosted on the sender's server instead of attached to the message. When you open the email, your mail app downloads those images. A tracking pixel uses that download as a signal. It is an image, usually 1 by 1 pixel and transparent, with an address that is unique to you and that message:

<img src="https://t.example-mailer.com/open/8f3a2c91d4e7.gif"
     width="1" height="1" alt="" style="display:none">

What it reveals

The moment the image is requested, the sender's server logs it. Because the code 8f3a2c91d4e7 belongs only to your copy of the email, the sender learns that you opened it and when, to the second. Each time you reopen the email, they may see another open.

The request also carries your IP address, which gives a rough location (often the city) and your network or company. The request headers name the mail app and operating system, so senders can tell whether you read on a phone or a computer. Sales tools turn this into alerts like opened 3 times, last on mobile.

Pixels are common in newsletters and marketing mail, and increasingly in one-to-one sales email sent from tools that add them automatically. The sender does not need your permission and you see nothing.

Pixels and link tracking

Senders usually track clicks as well. Links in the email point to the sender's tracking server, which records the click and then forwards you to the real page. A link that shows a long address on a domain like click.example-mailer.com before reaching the actual site is a sign of this. Blocking images does not stop click tracking, because the record is made when you click.

How to detect and block pixels

The most effective defense is to stop loading remote images automatically. Most mail apps have a setting for this. Images then load only when you ask, so a pixel cannot report an open you did not choose to reveal. The trade-off is that newsletters look plain until you load their images.

Some services hide part of what a pixel reveals. Gmail loads images through its own proxy servers, which hides your IP address and device from the sender, but the sender still learns that you opened the message. Apple's Mail Privacy Protection downloads remote content in the background through a relay when mail arrives, whether or not you read it, which makes open data from Apple Mail users unreliable.

To check a message yourself, view its source and look for img tags with a width and height of 1, images hidden with display:none, or image addresses that contain long random codes on a marketing or tracking domain.