If you use Aweber, you probably received a notice from them today (December 28, 2018) saying that they were turning off confirmed opt-in (also known as double opt-in) – but only for certain integrations with certain 3rd parties.

If you sell products online, and if you have a mailing list, you may find that you want to add products to your Paypal account for your mailing list API (such as the Aweber API) to use. For example, when you hook the Aweber API into Paypal, you can choose which mailing list the buyer of a given product gets signed up for by which product they have purchased.