Open tracking explained
How email tracking works
Email tracking tells you when a message you sent gets activity, so you can decide when to follow up. Almost every tool does it the same way: a tiny invisible image inside the email. This guide explains what happens when that image loads, why the result is a useful signal rather than proof of reading, and what you can realistically learn from it.
The tracking pixel in one paragraph
When you send a tracked email, the tool adds a 1×1 transparent image with a unique address to the message. The recipient sees nothing. When their mail app displays the email with images turned on, it asks the tool’s server for that image. The server notes that the unique address was requested and when. That request is the “open.” Nothing is installed on the recipient’s computer, and the image does not read their mailbox.
Can you tell if an email was read?
Not with certainty. You can tell that the tracking image was loaded, which usually means the email was opened on a screen. You cannot tell whether a person read it, how far they got, or whether they understood it.
Keep in mind. An open signal means the image loaded. It does not guarantee that the recipient read the message.
The only built-in alternative is a read receipt, which the recipient must agree to send. In Gmail, read receipts are available only on some Google Workspace accounts. See how Gmail read receipts work.
What can load the image besides a person
- Gmail’s image proxy. Gmail fetches images through Google’s own servers and may cache them. The sender sees a load from Google, not from the recipient’s device, and a later reopen may not trigger a new request.
- Apple Mail Privacy Protection. When it is on, Apple Mail can load remote images in the background before anyone opens the message. That produces opens nobody made.
- Corporate security scanners. Company mail filters often open messages and links to check them, sometimes seconds after delivery.
- You. Opening your own copy in Sent can load the image too, depending on the tool.
Good tools filter the automated loads they can recognize. None can filter all of them.
Why an email can show no opens
- The recipient has not opened it yet.
- Their mail app blocks remote images until they allow them, so the image is never requested.
- They read only the preview line in the inbox list, which does not display the message body.
- A cached image from an earlier load was reused.
So “no opens” means “no information,” not “ignored.”
Does previewing count as an open?
If the message body is displayed with images on, yes. That includes a reading pane next to the inbox. The one-line snippet in the inbox list does not load the image.
Can forwarded emails be tracked?
A forwarded email usually keeps the tracking image. When the new recipient opens it, the signal comes back to the original email, and most tools cannot tell who opened it. A burst of opens days later often means the email was forwarded or shared.
Link tracking and location
Some tools also rewrite the links in your email so they can record clicks, and some show an approximate location based on the IP address of the request. Because Gmail loads images through Google, location from Gmail opens mostly points to Google’s servers. SentCue does neither: it uses only the image signal, does not rewrite links, and does not keep recipient IP addresses.
What open tracking is good for
- Timing a follow-up. A fresh signal after a quiet week is a natural moment to write again.
- Knowing when to resend. No activity at all after several days can mean the email was missed or filtered.
- Prioritizing. If you sent ten proposals, signals help you decide which thread to follow up on first.
Use it as a hint for your next step, not as a verdict on the other person.
How SentCue shows it in Gmail
SentCue Email Tracking is a Chrome extension for Gmail on the web. A tracked email gets a small gray circle in Sent. When the image loads after the Undo window, the circle turns blue and shows the first and latest time and the count. Known automated loads are filtered. History and reminders stay in your browser, and no SentCue account is needed. Read what the colors mean or how to set it up.