Mailchimp is the world's leading email marketing automation platform. The integration for X-Cart is available in the add-on named Mailchimp Integration with eCommerce Support. It is a powerful tool that replaces the built-in newsletter subscriptions feature and enables you to access exciting eCommerce features like product recommendations, abandoned cart messages, purchase-based automation, and sales reports.
To start using Mailchimp in your store, make sure the Mailchimp Integration with eCommerce Support add-on is installed. See Installing Add-ons from X-Cart App Store for guidance.
The Mailchimp add-on requires an installed and enabled Newsletter Subscriptions add-on. If you use both add-ons simultaneously, the Newsletter Subscriptions add-on is linked to Mailchimp. As a result, your online store no longer records the subscriber email addresses submitted via the subscription form. Mailchimp handles them instead, provided you configured the Mailchimp Integration correctly and connected your online store to it.
Suppose your store has a list of subscribers formed by the Newsletter Subscriptions add-on when switching to Mailchimp. In that case, you should not expect Mailchimp to import these subscribers automatically. To use your existing subscribers with Mailchimp, you will need to export them from your X-Cart store and manually import them into your Mailchimp account. See more information on how to import subscribers into Mailchimp here.