How does one-click unsubscribe work technically? (List-Unsubscribe header)

One click unsubscribe works technically through List-Unsubscribe headers that mailbox providers process when users request unsubscription. The List-Unsubscribe header contains a URL (and optionally a mailto address) where unsubscribe requests should be sent.

The List-Unsubscribe-Post header indicates the sender supports POST requests, enabling true one click functionality. When a user clicks unsubscribe in their email interface, the mailbox provider sends an HTTP POST request to the specified URL with the body "List-Unsubscribe=One-Click".

Your server receives this POST request and must process the unsubscription, removing the recipient from future mailings. The URL typically contains tokens identifying the specific recipient and subscription. Responses should return HTTP 200 to confirm successful processing.