Create a non stock item (service) for each type of postage, assuming that you have a default price for each.
- To create a non stock item (service), go to Inventory > Parts.
- In the top right corner, click the drop down arrow and select New Service. Enter the relevant information as if it was a stockable product. Click Save when you've finished.
- If you want to create this within any document (SO, PO etc) use the drop down arrow near Create Part and select Create Service.
- When you add a service item to a SO, it will not show on the packing stage, nor will it show on a receiving stage from a PO