Mailchimp's e-commerce features work with a store object that is linked to a Mailchimp list.

The store object works with customers, orders, products, and temporary shopping carts. The connected list contains subscribers. Mailchimp uses the following logic:

• If a customer is added to the store object and does not exist as a subscriber in the connected list, this customer is created as a subscriber in the linked list. The subscriber status, which can be specified in the plugin, plays a role here. If this status is activated, the newly created subscriber is created as “subscribed,” which means that they can be contacted with marketing campaigns.
  If the subscriber status option is not activated, the customer is added to the list as a transactional subscriber and cannot be contacted with marketing campaigns. Subscribers with a transactional status can only be contacted via transactional emails, e.g., with the abandoned cart recovery feature. This is particularly relevant if you want to create an empty list of customers.

• If a customer is added to the store object and this customer already exists as a subscriber in the linked list, the subscriber status is not changed unless the subscriber is saved as a transactional subscriber. A subscriber who has the status “subscribed” and is then transferred again as a “transactional” subscriber by the plugin will not experience any change. If, for example, you want to enrich existing subscribers with their e-commerce data, it would be advisable to deactivate the subscriber status. This way, subscribers already in the list receive the additional e-commerce information from Shopware in Mailchimp, and customers who are transferred and are not subscribers cannot be contacted with a campaign because they are transferred as transactional subscribers.