Final answer:
The U.S. Postal Service's exclusive right to deliver first-class mail represents a legal monopoly, where the government allows only one provider to deliver essential services.
Step-by-step explanation:
The fact that under U.S. law, no organization other than the U.S. Postal Service is legally allowed to deliver first-class mail is an example of a legal monopoly. A legal monopoly is a situation where the government grants a single entity the exclusive right to provide a particular product or service. This is often the case with utilities and essential services that are crucial for daily life and where having multiple providers is not practical or beneficial to society.
These entities become regulated monopolies to ensure that these necessary services are available to consumers in sufficient quantities. Apart from being socially beneficial, such monopolies also enjoy economies of scale, suggesting that having a single provider can lead to cost savings that potentially benefit consumers.