Open rate is the percentage of recipients who opened a given email campaign. It is one of the most quoted email marketing metrics because it offers the first visible signal that your subject line, sender name and timing worked. The formula is unique opens divided by delivered messages (not by total sent), multiplied by 100.
How open rate works in practice. An open is registered when the recipient's email client downloads a tiny tracking pixel embedded in the message. That mechanism has a known limitation since 2021: Apple Mail Privacy Protection (MPP) pre-fetches the pixel for users who opt in, inflating opens for any audience heavy in Apple Mail. Industry benchmarks now sit around 20–30% across most B2C verticals; B2B and niche newsletters often run higher. Look at trend lines on your own list, not absolute numbers in isolation.
Why open rate matters for senders. Open rate is the first proxy for engagement, and engagement is what mailbox providers use to decide whether your next campaign reaches the inbox. A falling open rate is an early warning that your reputation, content or list quality is slipping — long before bounces or spam complaints catch up. Treat it as a leading indicator and segment your list around it: highly-engaged readers, lapsing readers, and inactive contacts each deserve a different sending cadence.
Mailpro and open rate
Real opens, in real time
Mailpro tracks opens per campaign and per contact, with MPP-aware reporting and historical trends — so you can react before a soft engagement dip becomes a deliverability problem.