2 Answers

The first post office in Boston—and probably in the first in America—was established in the home of Richard Fairbanks, on or very near the site of the [old] Boston Globe building in 1639.

Richard Fairbanks was an influential person in Boston, England, and had emigrated to Boston, New England with Reverend John Cotton in 1634

Site of First Post Office

I do not know exactly but it was prior to 1683 when William Penn granted to Henry Waldy, of Tekonay, the right to hold a weekly post between Philadelphia, Wilmington and Boston

In that year a law was passed at Philadelphia making every justice of the peace, sheriff and constable responsible for the speedy forwarding of such letters, "directed to or from the Governor," as should come to hand. It is possible that this service was soon after extended to the dispatch of private letters.