The discount code component works automatically with your Shopify store.  When your customer opens their email a unique one-time use discount is generated and added to the back end of your Shopify store and visible in your Shopify admin.

We use the customers first name and a random array of numbers and letters for each discount code so they are personalized. 

You can learn more about how to use discount codes here - http://spently.com/blog/how-to-include-unique-discount-codes-in-your-shopify-emails

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