Understand how to set up the MailChimp integration to sync. all your customers or just some of them.
From email address and name
Choose what email address and name that should be the sender information.
Synchronize all your customers
Next up it's time to determine whether you want to synchronize all your customers or only some of them. If you want to synchronize every single customer in your customer list just check off "Sync all customers under your MailChimp settings.
Synchronize some of your customers
If you're not interested in synchronizing all your customers you can make a customer group and add the customers you want to synchronize to MailChimp. By doing so, you make sure that you don't accidentally synchronize any new or existing customer to MailChimp that shouldn't be there as it requires you to actively add the customer to the customer group which is being synced to MailChimp.
If you want to synchronize specific customer by customer group, make sure that the checkmark in "Sync all customers" under your MailChimp integration is off.
Start by navigating to "Customers" in the menu and choose "Customer Groups" in the dropdown.
a. To create a new customer group that should be sync. to MailChimp, enter a name and check the "Sync this customer group's customers' e-mails to Mailchimp" and hit "Save.
b. If you already have a customer group with customers you want to synchronize to MailChimp, just hit the edit button on the desired groups and check the "Sync this customer group's customers' e-mails to Mailchimp" and hit "Save".
Once done you should see a button called "Sync with Mailchimp" next to the group you just created or edited. Hitting the button should synchronize the customer group with MailChimp.