The open rate is the share of delivered emails that were opened. It's measured with a tracking pixel: an open is counted when the reader's email app loads that invisible image.
Why it's unreliable now
- Apple Mail Privacy Protection loads images automatically, so every Apple Mail user counts as an open.
- Apps and company systems that block images record no opens at all.
- Security scanners open emails to check them.
So the same campaign can show a very high or a very low open rate depending on who's on the list.
What to watch instead
For cold email, the reply rate is the number that matters, and the positive reply rate (interested replies) even more. Open rates are still useful for spotting a big problem: a sudden fall to near zero across a campaign can mean emails are landing in spam. Then run an inbox placement test.