The possibility to offer subscription to a Sendy List on User Registration at the concrete5 site. The subscription is sent as a POST request after the user goes through the on_user_validate event, after clicking the confirmation E-Mail which simultaneously acts as a Double-Opt-In switch for the list.
You must install the composer dependencies before installing this addon. Visit https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies to learn more about this.
If you use the Community Store Add-On for your concrete5 project, you can offer billing_first_name and billing_last_name on the registration page and they will be added as "Name" to your Sendy List.
According to the european GDPR legislation, you need to offer the user sufficient information on how to unsubscribe from your list if wished so. This is your responsibility as a Mailing List Processor.