The Default Delivery Method selection criteria is used to indicate whether the resulting output should include Purchase Orders (POs) that have a particular Delivery Method specified (as defined on the Purchase Order >> Form page). You can choose to limit the resulting output to those having one, two or all three of the possible settings.   Leaving all three unchecked is equivalent to checking all three.

Regardless of the PO's default Delivery Method, the user can choose to email or print any PO.