You want to order a product from one or several vendors for one particular customer.
In contrast to mass orders for the general market, the product in the purchase-to-order is especially designed for the customer so that it cannot be sold to other customers.
The customer orders a material which is not in stock. Goods are procured specifically for this customer.
Saving the sales order triggers the creation of the purchase requisition automatically. No MRP-run is required in this case.
This process can also include some customer specifications to the material often referred to as "special make up" (SMU).
The requirement will be kept in a special MRP section. The stock will be received in the special stock segment "E - sales order stock".
Because this stock is customer specific it is not relevant for supply assignment processing (ARun) even if the material in general is set as ARun-relevant.