Jilt will send any customer a recovery email so long as the customer has added items to the cart and Jilt has captured their email address. Jilt can capture email addresses in four ways:
If a guest customer on your site has entered an email address at checkout, this will be recorded in Jilt and that email address will be used to send recovery emails.
If a customer enters their email address to the Early Email Capture popover when adding an item to the cart.
If a customer enters their email address to Jilt's popup signup form.
All registered users on your site have an email address, and thus any time a registered customer abandons a cart, Jilt will send this customer recovery emails.