Using Spently's follow-up emails allows you to engage with a shopper after they have purchased from you. To send follow-ups for orders that occurred before the follow-up email was set live, you will have to sync your past purchases.
You can only sync previous purchases on the Pro, Super, Elite, or Premier plans. Simply go to the Settings page, click on Company Settings, scroll to the bottom and click "Sync." You will receive an email once this process is complete.