Opt-out
The pattern where the subscriber is assumed to consent until they actively decline — legal in the US, illegal in most of Europe.
Opt-out is a consent pattern where the recipient is presumed to consent to receiving email until they actively decline (typically by clicking unsubscribe). The opposite is opt-in, where consent must be active before sending.
In the US, CAN-SPAM permits opt-out for commercial email — you can send to a recipient who hasn't previously consented, provided you include a working unsubscribe and other compliance requirements. In the EU (GDPR), UK (PECR), and Canada (CASL), opt-out is generally invalid for marketing email; consent must be opt-in.
For international senders, defaulting to opt-in for all lists simplifies compliance — you only need one operational model rather than segmenting by recipient geography. The marginal list growth from opt-out flows is usually less valuable than the regulatory exposure and reputation cost.