What Is an Opt-Out?

By suppressing the contact everywhere, not by removing them from one campaign. A contact who opts out of one sequence and receives the next one from a different sending mailbox has been ignored, and from their side it is the same company doing it twice.

A reply asking to stop is an opt-out even though no link was clicked. This is the case most often missed, because the request arrives as ordinary inbound mail and has to be recognised and recorded by whoever reads the replies.

A header-based opt-out defined in RFC 8058, where the client shows an unsubscribe control and the request is sent directly, so the recipient never reaches a landing page or a preference centre. Google and Yahoo have required it of bulk senders to their consumer domains since 2024.

It removes the friction that used to sit between annoyance and a spam complaint. A reader who cannot find the unsubscribe reports the message instead, and a complaint costs the sending domain considerably more than a lost contact.

In a suppression list that sits above individual campaigns and lists, so it is checked at send time rather than at import time. Storing the opt-out only as a removal from a list means the next import of a similar list quietly reinstates the contact.

It also has to survive a change of tool. An opt-out held inside one platform is lost on migration, and a sender who contacts a suppressed address after a migration has no record that the request was ever made.