Open tracking works by embedding a transparent 1×1 pixel image with a unique reference in each email. When the image downloads, an “open” is recorded. That mechanism is the whole problem.
Why the numbers lie
- False positives. Some inboxes fetch every image before delivery—malware scanning, and privacy features like Apple’s Mail Privacy Protection—firing “opens” no human performed.
- False negatives. Other inboxes block images by default, or sit behind corporate firewalls that cache them. Real readers, zero opens recorded. Gmail also clips messages over 102KB, and a clipped message doesn’t count as opened unless the recipient expands it.
- Structural blind spots. A plain-text email can’t be tracked at all—no HTML, no pixel.
Add it up and open rate is not a statistically honest measure of engagement. It can sketch a trend on a large marketing list; as an absolute number, it’s fiction.
The part that should decide it for you
Tracking pixels are the tooling of marketers—and of spammers. Inbox providers know this, and treat the presence of trackers as a signal that mail is promotional, which influences where it gets filed. That’s why the recommendation for transactional email is to turn open tracking off entirely: a password reset gains nothing from a pixel and shouldn’t smell like a campaign.
What to use instead
- Click tracking. A click is a real, deliberate act—if they clicked, they read. It’s a far more truthful engagement signal (route it through a custom tracking domain).
- Outcomes outside the inbox. Emails exist to cause something: signups, visits, conversions. Measure the something.
The verdict logic
Running a large marketing program and want directional trend lines? Fine—keep open tracking on and read it as weather, not measurement. Sending transactional mail, or making decisions off open rates? Turn it off and count clicks and conversions instead.