Hello! Klaviyo's abandoned cart email functionality can work for both logged-in and guest customers.

For logged-in customers, Klaviyo can automatically track their abandoned cart behavior and send them an email reminder to complete their purchase.

For guest customers, Klaviyo can use browser cookies to track their abandoned carts and send them an email reminder to complete their purchase. However, in order for this to work, the customer needs to provide their email address during the checkout process.

So, it is not necessary for customers to have an account or be logged in for Klaviyo's abandoned cart functionality to work.