One-click unsubscribe

One-click unsubscribe uses two headers. 'List-Unsubscribe' holds a web address (and often a mailto address). 'List-Unsubscribe-Post' holds the value 'List-Unsubscribe=One-Click'. Together they tell the mailbox provider that it may send a request to that address on the user's behalf. The provider then shows an 'Unsubscribe' button near the sender name, and one click removes the person without a web page.

Gmail and Yahoo ask bulk senders to support it for marketing mail and to act on requests within two days. It also matters for cold email, because a visible exit is better than a spam complaint. Keep a plain unsubscribe line in the body as well.

Common mistakes: sending the headers without a working endpoint, an endpoint that needs a login, headers that are not covered by the DKIM signature, or an unsubscribe that does not stop later steps in the sequence. Test the link, and make sure an unsubscribed address is added to your suppression list.