Open rate

Open rate is measured via a tracking pixel embedded in the email — when the recipient's mail client loads images, the pixel fires and we record an "open."

iOS 15+ and most modern mail clients pre-fetch images for privacy reasons, which inflates open rates with false positives. Apple Mail Privacy Protection, in particular, makes open rate roughly meaningless for B2C senders.

For cold B2B, open rate still has signal — but reply rate is the metric that matters. BoomSauce templates default to no images on first touch precisely because the open-rate signal isn't worth the deliverability cost of including them.