Your own sign-up forms post to stet; each person is recorded in your own Postgres with a one-click unsubscribe.
A site’s sign-up form posts to stet, and stet records who joined which list,
when and from which page, in your own database. Every email can carry a
one-click unsubscribe that stet serves, and your own provider does the
sending. stet contacts shows a list’s members and one person’s record, and
exports or erases a person on request.