Open rate

Open rate is the number of messages recorded as opened divided by the number delivered. The recording works through a tiny invisible image loaded from the sender’s server when the email is displayed; the request for that image is counted as an open. It has been the headline metric of email for decades because it is easy to compute and looks like attention.

It matters less than it used to, and understanding why protects you from bad decisions. Many mail clients block remote images by default, so real reads go unrecorded. Apple Mail Privacy Protection does the opposite: it pre-loads images on Apple’s servers whether or not the person reads the message, so opens are recorded for people who never looked. Corporate security gateways scan links and images before delivery, producing opens and clicks from machines. The result is a number that moves for reasons unrelated to your subject line. Replies, meetings and proposal reads are the signals worth steering by; opens are, at best, a rough check that mail is being delivered.

In Seegnals opens and clicks are tracked only through a custom tracking domain you own; without one, they are simply not tracked and the interface says so. Open rates are shown with a note about Apple Mail Privacy Protection inflating them.