United States Postal Service (USPS) The USPS is the independent postal service of United States government, offering domestic and international shipping services by land and air. Once the USPS module is setup your customer’s can select from a list of USPS delivery services and have the shipping automatically calculated during checkout.
Please Note: For each product that you want to have the shipping cost automatically calculated during the checkout process you must select “Per Weight” for the shipping method and enter values in the “Weight” and “Weight units” fields when adding the product to your store. Click here for details.
You will need to register with USPS in order to obtain an USPS Username and Password. This allows you to connect to the USPS shipping cost calculator.
After you complete the registration process, you will receive your User ID and a URL to the USPS test server. You can skip the testing phase, and contact their Internet Customer Care Center to request immediate activation to the production server. The Customer Care Center will validate your store and provide you an API Username and API Password.