What is email open rate?

Email open rate measures how many delivered messages were opened at least once. It reflects interest, visibility, and how well your sender reputation keeps you in the inbox rather than the spam folder.

This metric’s reliability was permanently altered by Apple Mail Privacy Protection (MPP), introduced in 2021.

It is a surface level signal. It tells you who lifted the lid of the message, nothing more. Behind the scenes, the number is shaped by image loading, privacy tools, and caching decisions rather than pure human behavior.