Unsubscribe rate

It is both a legal number and a health check. Rules such as GDPR and CAN-SPAM require opt-outs to be honoured promptly, and large mailbox providers expect bulk senders to offer an easy one-click unsubscribe. Beyond the rules, a rising rate is an audience saying, plainly, that the emails have stopped being worth opening.

Left unwatched it also does damage. Mailbox providers lower a sender's reputation when enough people leave or complain, and a damaged reputation sends future emails to spam whatever the content.

• Watch the trend for each send and each list, not only the overall average. Benchmarks vary by industry, so compare against your own history first.
• When the rate spikes, look for the specific change: more frequent sends, a new audience, content that drifted, or a stale list.
• Segment the list so people only receive what is relevant. Sending everything to everyone is one of the fastest ways to push the rate up.
• Make the unsubscribe link easy to find. Hiding it moves people from unsubscribing to marking the email as spam, which is far worse.
• Remove people who never open on a regular schedule, instead of waiting for them to leave.

Take the number of people who clicked unsubscribe after a send, divide by the number of emails delivered, and multiply by 100. If 1,000 emails were delivered and 3 people left, the rate is 0.3 per cent. It is measured per send, and also across a month to see the trend.

• Treating a very low rate as proof that all is well. People who stop reading without unsubscribing are not counted.
• Mixing up unsubscribes with spam complaints. An unsubscribe is a polite exit. A complaint is what actually damages sender reputation.