Opt-in lists track audience members who check the opt-in checkbox on your forms or polls. The "All opt-ins" list contains every audience member who has checked an opt-in checkbox on your embeds. If you use Hearken's Mailchimp integration, that will pull from that list.

Click "View Details" and then use the Download CSV option to export opt-in lists so you can upload them into your own systems to subscribe them to communications from your organization:

By default, every new form you create contains an opt-in checkbox inviting submitters to sign up for your newsletter. Each form can only have one opt-in checkbox at a time:

You can customize the copy or hide the checkbox altogether in the embed features section of the embed's settings. You can also choose which opt-in list or lists to associate people who check the box with:

If no opt-in list is chosen, submitters who check the box will still be added to the default All Opt-Ins list (along with everyone else who checks an opt-in box).