One-click unsubscribe

List-Unsubscribe carries the addresses that can process a removal — a URL, a mailto, or both. List-Unsubscribe-Post carries the value that tells a client the URL accepts a direct POST, which is what makes the removal one click rather than one click and a landing page.

Sending the first without the second gives you a button that opens a browser. Sending both gives you the behaviour the providers are actually asking for.

The alternative to an easy unsubscribe is the spam button. One is a quiet removal from your list; the other is a complaint recorded against your domain and weighed heavily by every provider that saw it. Making the exit obvious is the cheapest complaint-rate control available.

It also improves your data. A person who unsubscribes has told you something specific; a person who marks you as spam has told the provider something much worse and told you nothing.

The endpoint has to accept an unauthenticated POST from a mail provider's infrastructure, act immediately and idempotently, and return quickly. It must not require a login, a confirmation step or a preferences page — a confirmation flow behind a one-click header is the most common implementation error and it results in unsubscribes that never take effect.

Keep the hosted page too, for clients that do not support the header, and have both write to the same suppression list.

SalesShift serves a hosted unsubscribe page and accepts the RFC 8058 one-click POST at the same address. Both write to the workspace suppression list, which is checked before every subsequent send.