The two headers

List-Unsubscribe carries one or two targets in angle brackets: an https URL, a mailto address, or both. List-Unsubscribe-Post: List-Unsubscribe=One-Click tells the mailbox that the https URL accepts a POST request and will process the unsubscribe immediately without a login, a confirmation page or a survey. Together they are what RFC 8058 calls one-click unsubscribe, and what Gmail and Yahoo have required of bulk senders since 2024.

What the mailbox does with them

Gmail shows an “Unsubscribe” link beside the sender name. Apple Mail shows a banner at the top of the message. Yahoo does both. When the recipient taps it, the client POSTs to your URL — not a GET, which crawlers and security scanners trigger by accident — and expects the address gone within two days. A visible link in the body is still required; the header is in addition to it.

Where it does and does not belong

Marketing, newsletters, product updates, anything subscribed: required. Transactional mail such as receipts and password resets: not required and usually inappropriate. One-to-one cold outreach from an individual mailbox: not covered by the rules, and adding the headers to a message that reads as a personal note is incongruous. The right pattern there is a plain sentence offering to stop, and honouring every reply that asks. What matters to reputation is that the recipient has an easy way out that is not the spam button.

Check yours

These run free in your browser. Nothing you type reaches a server.

Common questions