Open rate is calculated as (Unique Opens ÷ Delivered Emails) × 100. It is one of the primary engagement metrics for newsletter creators. Industry benchmarks for creator newsletters typically range from 35–55% for engaged lists, though rates vary significantly by niche, list age, and sending frequency. Apple Mail Privacy Protection (MPP) inflates open rates because emails are marked as opened when pre-fetched — treat open rate as a directional metric, not an absolute truth. InfluencersKit tracks opens alongside click rate and revenue metrics for a fuller picture.