Difference between opt-in and double opt-in

Difference between opt-in and double opt-in

Email addresses on a 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. This request for confirmation is sent to the submitted address and the address owner must take some action to confirm that the user is the owner of the email address, and the address is working.