美国邮政部门的警察正式名称叫什么？

是叫United States Postal Police，译为美国邮政警察，是美国邮政检查局下的一个分支。
局里的网站介绍说其职责为保护美国邮政系统的安全并保证邮政系统的公信力（大概就是邮件正常投寄收取不受威胁、邮政系统正常运行之类）全局共有650名制服警官分布在各大小邮局；还有1500名邮政监察员对邮件进行例查以保证公共安全以及邮政安全。该分支直到1970年邮政系统建立才独立出来；之前一直被称作美国州署邮政警察。

下面是网站简介原文
United States Postal Police

About this Agency
The United States Postal Police is a division of the United States Postal Inspection Service.
The United States Postal Inspection Service mission statement is as follows: to protect the U.S. Postal Service, secure the nation's mail system and ensure public trust in the mail.
The 650 uniformed officers of the United States Postal Police are stationed around the country and responsible for ensuring the safety of critical postal facilities and their employees. The officers also share responsibilities such as escorting high value mail, perimeter security, and other protective duties. In addition to the United States Postal Police, there are more than 1,500 postal inspectors -- they are responsible for "enforcing more than 200 federal laws covering investigations of crimes that adversely affect or fraudulently use the U.S. Mail and postal system."
The United States Postal Police agency was not formed until the Postal Reorganization Act of 1970. Before being known as the United States Postal Police, officers were referred to as Security Aides and later Security Police Officers.

除了上面的介绍以外维基百科还介绍说邮政警察还负责协查诈骗（邮寄件）；外部安全（信件被非邮政人员偷窃和邮政人员安全）；违禁物品邮寄调查；航空和国土安全，收入调查，国际调查和全球安全以及与其他部门的联合调查（以上应该都指邮政方面。）