To allow Shopify to send emails on your behalf you will have to add it to your SPF record. The SPF record mechanism used for Shopify is shown below.

include:shops.shopify.com

DKIM

To setup DKIM for Shopify, you can authenticate your domain by clicking Authenticate on the Sender email page of your Shopify admin console. A new window will open and provide you with instructions on how to create four new records with your domain provider.

Create a free OnDMARC account to test your configuration.