When migrating to ReCharge, if the customer doesn’t already exist on your store, then we will add the customer to the Shopify store when the customers are imported to ReCharge. This creates the account and adds the email address. The customer will still need to register their email address and create a password. Here is an article on how to invite customers to register their accounts.
If the account already exists in the store on another platform, then we just sync the ReCharge account with the Shopify customer’s email.