Others talk about "double opt-in" (or "confirmed opt-in") as if it was a completely different matter. But is it?
The Difference Between Opt-In and Double Opt-In
- Email addresses on a (single) opt-in list are not confirmed. Anybody can submit anybody's address to the list, and it will be there until it is unsubscribed.
- On a double opt-in list, all email address must be confirmed before they are added. A request for confirmation is sent to the submitted address and the address owner must take some action to confirm that
- she is the owner of the email address,
- the address is working and
- she indeed wants to subscribe.