Open rate
The percentage of delivered emails with a tracked open, subject to privacy features, image blocking, and provider definitions.
Open rate is the share of delivered emails that registered an open. It is tracked with an invisible pixel, which is exactly why it broke: Apple Mail Privacy Protection preloads messages on Apple’s servers, registering opens no human made. Lists heavy in Apple Mail readers can see rates inflated far beyond real behavior.
Open rate still earns a place as a directional signal. A change may warrant investigating delivery, tracking, or audience differences. Subject-line comparisons need consistent audiences and measurement conditions. Just avoid treating the absolute number as a count of humans, and lean on clicks when you need evidence of real attention.
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