Shopify is showing that Duoplane sent a shipping confirmation email to my customer—how do I disable this?

This may be the result of a misconception of how information is transferred between Duoplane, Shopify, and your customer. Duoplane does not reach out directly to your end customer to notify them of a shipment. If you see order notes in your Shopify that look similar to the below, what this means is Duoplane had updated Shopify, which then notified your customer based on communication preferences you have set within Shopify.

The only time Duoplane will reach out to a customer of yours directly is for return instructions or a promise date adjustment (if given permission to).