When setting up a new subscriber list, you have the option of creating either a single opt-in or confirmed opt-in. The type of list you should choose depends on the quality of the list you require as well as the quantity of subscribers you are hoping to attract.
Single Opt In
Single opt in means that as soon as a subscriber completes a subscriber form, they are automatically added to that Subscriber List. No additional confirmation or step is required.
Confirmed Opt In (sometimes known as double opt in)
Unlike single opt in, confirmed opt in requires your subscribers to validate their email address before being added to your subscriber list. When a new subscriber completes the subscribe form on a web site, an email is immediately sent to the address they provided. This email contains a verification link which the recipient clicks on to confirm that they own the address. Once the link has been clicked, that email address is added to your list.
If the link is not clicked, then the subscriber is not added. If they later fill in the subscribe form again, they will be sent another verification email.
The type of list you select for each client completely depends on your requirements. Listed below are some of the advantages and disadvantages of using confirmed opt-in Subscriber Lists:
Advantages
Disadvantages
For all of your subscriber lists, you can completely customize the single and confirmed opt-in process by entering your own URL for custom confirmation pages and also editing the contents of the verification email.