Abandoned carts
With the Sync carts option of the Exclusion tab, the cart of an identified customer is sent to Mailchimp at every change, then removed from it once the order is placed. Your Mailchimp abandoned cart automations thus have the products, the amounts and a link back to the cart.
Abandoned cart automations are part of the Mailchimp e-commerce features: they require a paid plan and an associated store, with the catalog synchronized.
A signed recovery link
The link in the email only carries the cart and a signature computed with a secret key of your shop: it cannot be forged. It expires after 14 days, or as soon as the customer changes their password. A link that is no longer valid leads to the login page.
Automatic connection of clients
With this option, the link also signs the customer in to their account. Anyone who receives the email, forwarded for instance, then opens the account: the option is off by default. Without it, the visitor finds their cart and signs in at checkout.
Performance
If you do not use abandoned cart automations, turn off cart synchronization: adding to cart gets faster.
