1. In the administration panel, go to Administration > Shipping & Taxes > Shipping methods.
  2. Create a shipping method or choose the existent one.
  3. Click on the name of the shipping method to modify it.
  4. Select Realtime in the Rate calculation field, select USPS Express Mail (or another service) in the Shipping service field.



  5. Open the Configure tab and set up the necessary options there. Fill your USPS credentials in the User ID field. If you do not have any, you need to sign up for the USPS User ID here.



    NOTE:
    1. You should confirm your USPS User ID before using it. You should call USPS (800-344-7779) to activate your account on the production servers. It will not work until you do this.
    2. Only some specific requests for retrieving shipping costs work properly if the Test mode option is enabled.
  6. Open the Shipping charges tab and define shipping charges which will be added to the ones returned by real-time shipping service  if it is needed. Click the Save button to save the changes.
  7. Open the General tab, enter the desired value into the Weight (lbs) input field and click on the Test link next to the Shipping service field to make a test calculation of shipping charges.