Definition
Open rate is the percentage of delivered emails that were opened.
open rate = opens ÷ emails delivered × 100
How opens are tracked
A tiny invisible image (a tracking pixel) is added to the email. When the email client loads it, the open is recorded.
Why it's unreliable
- privacy features in some email apps pre-load images, recording opens that never happened
- image blocking hides real opens
- security scanners open emails to check links
So open rates can be inflated or deflated, and don't reliably show interest.
Deliverability concerns
Some senders believe tracking pixels and tracked links make emails look more like marketing, which may affect inbox placement. Many cold emailers turn open tracking off.
What to measure instead
- reply rate and positive reply rate
- meetings booked
- bounce rate (list quality)
- spam complaints (if your tool reports them)
Use opens only as a rough, relative signal — for example, comparing two subject lines on the same audience.
Example
A campaign reports a 70% open rate but only 1% replies. Some of those "opens" may be privacy features loading images automatically — the reply rate tells you more about real interest.
Key takeaways
- Opens are tracked with a hidden image.
- Privacy features make opens unreliable.
- Measure replies and meetings instead.