Shopify includes notification options that email customers when the status of their order has been updated. If you have opted to writeback the status to Shopify, you may need to consider whether your customers are receiving duplicate notifications. You can then enable/disable notifications, as required.
This article outlines how to disable Shopify customer notifications in DHL Express Commerce.
Deactivate Shopify notifications
In DHL Express Commerce, navigate to Settings > Integration > Shopify > Advanced tab.