List-Unsubscribe is an email header that tells the inbox how to unsubscribe the reader, so Gmail, Yahoo and Apple Mail can show their own unsubscribe button next to the sender.
How it works
The header sits in the email's headers, not in its body. It holds a way to unsubscribe: a web address, an email address, or both. A second header, List-Unsubscribe-Post, makes it one-click (RFC 8058): the inbox sends a single POST request to the web address and the person is unsubscribed, with no page to visit.
List-Unsubscribe: <https://your-mimeo.com/u/SIGNED_TOKEN>
List-Unsubscribe-Post: List-Unsubscribe=One-Click
Both halves matter. Without List-Unsubscribe-Post, a mail client shows a link rather than its own unsubscribe button. Gmail requires one-click unsubscribe on marketing email from anyone who sends more than 5,000 messages a day.
Why it matters
- Fewer spam complaints. A reader who can unsubscribe in one tap doesn't need the spam button.
- Inbox placement. For bulk senders, Gmail's sender guidelines make one-click unsubscribe a requirement, not a nice-to-have.
- It has to work at once. The unsubscribe should take effect straight away, so the next email never reaches the person.
How Mimeo handles it
Mimeo sets both headers on every broadcast and sequence send, pointing at your own Mimeo. (Postmark's broadcast streams replace them with Postmark's own until you turn on custom unsubscribe handling; see Postmark setup.) When a mail client uses the button, Mimeo handles the request itself: a valid token always unsubscribes the person from everything, and the unsubscribe is recorded against the exact email it came from. See one-click unsubscribe in the API docs, and Mimeo terms for unsubscribes and suppression in Mimeo's own words.
- Email sender guidelines. Checked .
- Subscriptions API. Checked .