In the late eighteenth century, postmasters received, sorted, and distributed mail from taverns, coffeehouses, print shops, and even old churches. Stand-alone post office buildings were uncommon; rather, post offices were an integral part of multi-use buildings.
As the nineteenth century progressed, post offices became notable single-use buildings that were often the architectural centerpieces of villages, towns, and cities. Many post offices were built in a classical style that reflects their link with the federal government, but other post offices took on the look of their local community.
During the twentieth century, as the volume of mail exploded, the mail could not be sorted in a single place. The postal service created small sub-station post offices, with regional mail being sorted in larger, centralized sorting centers.
Allison Marsh, National Postal Museum