Definition
List-Unsubscribe header
A hidden email header that lets mail clients show their own unsubscribe button and tell you when it is pressed.
The List-Unsubscribe header is a line in the technical part of an email, invisible in the body, that tells the receiving mail client how a reader can stop receiving messages from you. It can contain a mailto address, an https URL, or both. When it is present, Gmail, Outlook and others can show an Unsubscribe link next to the sender’s name, so the reader does not have to hunt through the footer. A companion header, List-Unsubscribe-Post, enables the one-click variant defined in RFC 8058, where the client sends a POST request and the reader is removed without opening a page.
It matters for two reasons. Recipients who want to leave use the button instead of the spam-report button, and a spam complaint hurts your domain far more than an unsubscribe does. And providers now expect the header from anyone sending in volume; without it, a sender is treated with more suspicion. For cold email it also demonstrates the respect for objection that legitimate interest depends on.
Seegnals adds one-click unsubscribe headers (RFC 8058) plus a visible unsubscribe link to every message. A reader who unsubscribes goes onto your suppression list, and the sequence stops for that person.