I'm setting up an abandoned cart “newsletter” in 2.2.3. It will be sent when the abandoned cart is 1 day old. Is it necessary (or possible) to include an unsubscribe link?
Somewhat a function of your site configuration. But basically, if there's an 'user_id' that is non-zero in the order data, then it is a registered user and you might want to include the unsubscribe link. But you might just be complicating things. If you only send once a day and the age of the abandoned cart is between 24 and 48 hours old then you probably don't need an unsubscribe link.
But note that generally, about 90% of abandoned carts do not have any contact info (unless you require registration to add to the cart) and so the number of users you're going to hit is pretty small.