At the bottom of every email there are two links: stop watching this one app, or stop all mail from us. Both work in one click and neither asks you to sign in first.
Your mail client's own unsubscribe button works too — we support the standard one-click header, so Gmail and Apple Mail can do it without opening anything.
Unsubscribing from everything is remembered permanently. We will not mail that address again even if somebody later tries to add a watch on it.