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]
Government procurement in the United States The authority to purchase is not one of the explicitly enumerated powers given to the Federal Government by Section 8 of Article One of the United States Constitution, but courts found that power implicit in the Constitutional power to make laws that are necessary and proper for executing its specifically granted powers, such as the powers to establish post offices, post roads, banks, an army, a navy, or militias.