I don't know the best practice but this one I have setup my UTM tags for my eCommerce site
For New Account creation
- Campaign Source : website
- Campaign Medium : email
- Campaign Name : new_account_email
- Campaign Content : hyperlink / calltoaction / confirm
For Shipment tracking email
- Campaign Source : website
- Campaign Medium : email
- Campaign Name : order_shipped
- Campaign Content : hyperlink / calltoaction / confirm
Please Note: And the end of the day all fields naming does not matter because you'll be knowing for want campaign you are running those email, etc, etc.
Hope this helps!