A custom object is the most appropriate persistent data structure because the requirement applies toboth registered and guest shoppers. A Profile-based solution cannot satisfy the requirement reliably because anonymous/guest customers do not have a persistent registered customer profile. Storing customer email lists directly on Product records would also create an inappropriate product-to-shopper coupling and potentially large mutable collections on product system objects.

B2C Commerce custom objects are intended to extend the persistent commerce data model for application-specific requirements. Developers can define custom object types with custom attributes, including multi-valuedSet of Stringattributes, and choose organization or site storage scope.

A custom back-in-stock object can therefore persist the shopper's email address plus one or more interested SKUs independently of authentication status. Subsequent job or inventory-update logic can identify subscriptions when inventory becomes available and trigger the notification process.

This design also keeps notification-subscription data separate from core customer and product objects, reducing unintended effects on standard platform data models and supporting anonymous shoppers cleanly.

Study Guide reference:Data Management Using Business Manager Usage --- custom object types, custom attributes, persistent business data, guest shoppers, and application-specific data modeling.

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