Who is in charge of mail processing within the USPS?

The United States Postal Service (USPS) is the correct choice because it is the federal agency responsible for providing postal services in the United States. This includes overseeing all aspects of mail processing, which encompasses the collection, sorting, and delivery of mail and packages. The USPS operates numerous facilities dedicated to these processes, ensuring that mail is handled efficiently and delivered in a timely manner.

In contrast, third-party delivery services and private courier companies operate independently and are not responsible for the mail processing functions of the USPS. While local post offices are part of the USPS and play a role in the delivery and dispatch of mail, they do not oversee the entire mail processing system; that responsibility lies with the USPS as a whole. Therefore, the United States Postal Service is the correct answer as it encompasses all aspects of mail processing within the organization.