Single or double opt-in?

Should you send a verification message before a sign-up counts? It costs volume and gives a lot back.

Single opt-in

The address typed goes straight onto the list. More sign-ups, but also typos, disposable addresses and sign-ups made by other people.

Double opt-in

A message with a link to click. You lose a share of sign-ups and gain a list where every address genuinely works.

What it changes in practice

Fewer bounces, fewer complaints, better deliverability for everybody. On an older list that difference shows in the first campaign.

The forgotten protection

Double opt-in stops somebody signing up another person's address. Without it you send to people who asked for nothing — and they complain.

How to limit the loss

Send the verification immediately, with a clear subject, and say on the sign-up page that it must be confirmed. Most drop-off comes from people who did not know they had to click.