1.安装United States Postal Service
2.登录https://registration.shippingapis.com/，注册帐号，稍后会收到邮件
3.打开邮件，记下User ID (Username)
4.配置下面内容
opencart配置United States Postal Service快递
原文：http://www.cnblogs.com/chixiaobai/p/5583720.html
