Outbound Glossary
Reply rate
The share of recipients who answered. Harder to fake than opens, though out-of-office replies and security scanners answer too.
Reply rate is replies divided by messages delivered. Unlike opens it usually takes a person to act, which is why we steer campaigns by it. Usually, not always: out-of-office messages, mail gateways and security scanners all produce replies with nobody having read anything, so the raw number is not purely human.
Read it with the positive and negative split visible. A four percent reply rate made of interest is a working campaign; the same rate made of people asking to be left alone is a campaign doing damage. Any tool that reports one number without that split is hiding the thing you need.