Reader of the month

The mistake

The unsubscribe endpoint writes the submitted address into the subscribers table instead of removing it, because the handler calls the subscribe path rather than the delete path. Since the address is already present, the upsert refreshes the record and re-confirms it as an active subscriber, so every unsubscribe click renews the signup. Repeated clicks also create duplicate list memberships, which multiplies how many copies of each send that address receives.