Security software can make an email look opened
There is a slightly awkward problem with open tracking: sometimes the first thing to load the image is not the person the message was sent to.
Business mail often passes through filtering systems before it reaches an inbox. A filter might inspect links, attachments, and outside content while deciding whether the message looks suspicious. If it happens to request the tracking image, the sender's system can record activity even though the employee has not looked at the email yet.
Forwarding can produce something similar.
The tracking image may remain inside the forwarded copy. If somebody else opens that copy, or if their mail service fetches its images, the original tracking address can be contacted again.
From the sender's side, these events are difficult to untangle. There was a request for the image; who actually caused it is another question.
That is one reason I would be careful about reading too much into the exact time shown beside an "open."
Open rates still have a use
This does not make open-rate statistics worthless.
For a newsletter sent to thousands of people, a large change from one campaign to another can still be interesting. If image requests suddenly fall well below the usual level, the sender has learned something about how that mailing performed.
The trouble starts when the same number is treated as a precise record of an individual reader.
An image may load when somebody opens the message, but it can also be loaded earlier by a privacy service or security system. Some clients cache images. Some people block them. Forwarded mail can create another request. Different mail apps handle all of this differently.
So I would treat an open rate as an approximate campaign measurement. It is much less convincing as proof that one particular person read one particular email at a particular moment.
Remote images can simply be left unloaded
Traditional tracking pixels need the mail client to request an outside image.
If that request never happens, that particular pixel has nothing to report from the client.
Many mail apps therefore give you some control over external images. One may leave them hidden until you click a button; another can ask before downloading outside content.
The downside becomes obvious if you read many newsletters.
A lot of ordinary email is built around images hosted elsewhere. Product photographs disappear, logos may be missing, and some messages end up looking half empty.
There is no requirement to make the same choice for every sender. Someone who wants more privacy could leave outside images blocked for unfamiliar messages and load them when there is a reason to trust the sender.
Look at the mail app first
Before installing another privacy tool, I would check the settings already available in the email application.
The names vary. One program may talk about remote content, another about external images, and another about protecting mail activity or hiding network information.
They are not all implementing exactly the same thing, so the description beside the setting matters more than its name.
Built-in controls also have a practical advantage: there is no additional extension or service involved simply to decide whether an image should load.
The useful thing to remember about a pixel is fairly modest.
At some point, a server received a request for an image.
That is the part you know.
You may have opened the message and caused it. The mail app may have fetched the image earlier. A security scanner, proxy, or forwarded copy may have been involved instead.
A sender can combine that event with other information and make an educated guess, and sometimes that guess will be a good one.
The request itself is still only a request.
It does not provide a recording of somebody sitting down and reading the email.