More often than not, depending on the settings of your Shopify store, the customer leaves their email address. This address can further be used not only to send notifications about the order status, but also to send email sequences aimed at repeating sales.
With this feature you can divide your contact list into groups and send emails with more products and promo codes at different intervals of time. For example, the email may be sent after 1 hour from the time of purchase, after 1-2 days, or after product delivery.
You will also be given detailed statistics for each campaign sent. It will include delivery speed, spam reports, link clicks, unsubscribes and etc. Apps such as Omnisend, Klaviyo, SmartrMail, Seguno can be used to automate the process of email marketing.