What is the best retargeting method for add to carts on shopify?

• Automated mail followups for abandoned carts • Upselling or promoting impulse purchase on add to cart/checkout page • Retargeting via fb ads (the recent products they viewed)

What's a good program for email follow ups ?

Automated mail follow ups with a discount code maybe if they left their info. If not, then fb and google display ads retargeting. Feel free to DM and I'll walk you through the exact process