A Special Order sales order line is special ordered for the customer from the vendor. The line is received in house, then shipped back out to your customer from your warehouse. The special order fulfillment method can only be used for stock items (order lines for nonstock items may not be flagged as special order).
When a sales order line is flagged as a special order line, and it is saved, the system creates a po requisition linked to the sales order line. This po line is used to order the required item and quantity from the vendor. When the po line is received, the system allocates the received inventory directly to the sales order it is associated with. The sales order is then completed from your warehouse. This method is similar to a vendor shipment in that po lines are created for the sales order, and linked to the order, and that the system restricts editing of the documents once they have been created.
Note: A single sales order line cannot be flagged as both Special and Vendor Shipment.
Special Order is a fulfillment method or process used to complete customer sales orders. When a Special Order sales order line is created on the system (due to the item being set up for special order processing only, or due to the operator setting the Special Flag to Y on the sales order line), the system creates a purchase order requisition specifically for the sales order line. This PO requisition - which is linked to the sales order line, is later converted to a special order purchase order line. Once the item(s) that are being special ordered are physically delivered to you by the vendor, the special order purchase order line is received into inventory, and then preferentially allocated to the special order sales order line that it was created for. (The system will allocate the items from the special order PO line to the sales order line that it was created for as long as the line is still open and as long as the sales order is not printed when the receipt is processed). The special order option can be used for items which you do not wish to order from a vendor unless you have a specific sales order in hand for the item, and to handle other situations.
Special Order Processing is discussed in detail in the documentation for the Purchasing System and this section provides only a brief discussion of how special orders are processed by the inventory reconciliation and inventory allocation routines.
More:
Special Order - Sales Order Entry
Special Order - PO Requisitions