Double Opt-In

After submitting the squeeze page form (single opt-in), a double opt-in sends a confirmation email; the person must click a link in it before they're officially subscribed. Anyone who doesn't confirm never joins the active list.

Double opt-in loses some subscribers at the confirmation step, but it also filters out fake or mistyped addresses and keeps your list quality higher — which matters a lot with traffic-exchange and safelist traffic, where a share of sign-ups are low-intent surfers. Most autoresponder services require it anyway to protect deliverability.