Open Rate
Definition
The percentage of recipients who open an email, used as a key email marketing metric.
Example Use Case
A nonprofit organization improves its email open rate by personalizing subject lines.
Open rate measures how many recipients opened a message, and it has long served as the headline number in email reporting. It is most useful for comparing subject lines and send times against your own past results, since it reflects the appeal of the subject line rather than the content of the email.
Its reliability has weakened over time. Privacy features in several major mail clients now load tracking pixels automatically, which records an open that never happened, so measured open rates can overstate reality by a wide margin. Comparisons across different audiences or different tools are therefore unreliable, even when the numbers look precise.
Treat it as a directional signal with a known bias. Where the decision matters, pair it with click rate and with what recipients actually do after arriving at the site, because a high open rate on a message nobody acts on is not success.
