Grouping uses the ingredient's Supplier Default. Ingredients without a default supplier fall into the No supplier group, which has no email button. Use the pencil next to the ingredient in the report (or the Supplier cell in the Ingredients list) to assign one. An ingredient with a supplier can still be missing from the email if its Total Needed is zero or negative, meaning your recorded stock already covers the requirement; check the Stock column and adjust it if the on-hand figure is out of date.