。
The postal service is a government monopoly.
Literal
Postal-business [topic-は] government-of monopoly-business is-[polite-です].
Formal-register compound-heavy statement. 郵政事業 ('postal services business') pairs 郵政 (post affairs) with 事業 (enterprise, undertaking). 独占事業 ('monopoly business') is a standard economic term. The sentence reads like a textbook definition or civics explanation.