who has the power to establish post offices
Postal Clause Article I, Section 8, Clause 7 of the United States Constitution, known as the Postal Clause or the Postal Power, empowers Congress "To establish Post Offices and post Roads".[1]
United States Postmaster General The Postmaster General of the United States is the chief executive officer of the United States Postal Service; Megan Brennan is the current Postmaster General. The office, in one form or another, is older than both the United States Constitution and the United States Declaration of Independence. Benjamin Franklin was appointed by the Continental Congress as the first Postmaster General in 1775, serving just over 15 months.