The building features an exterior in a monumental style, typical of the Fascist architecture, while the interior is characterized by a closer alignment with the modern principles of Italian rationalism.

Expropriations began in April, and demolition of existing buildings, including the recently built Art Nouveau-style Palazzo Barth, started in September.

[2] Post-war modifications included raising the central body of the building in 1953 (completed in 1955), constructing a new single-story section for mail carriers in 1963, and expanding the public hall and director's apartment in 1975.

It has a trapezoidal plan due to the plot's shape, leading to an unconventional layout along the bisector of the angle formed by the adjacent streets.

This section is connected to two nearly symmetrical wings along Via Roma and Viale Matteotti, with central spaces linking them and overlooking a rear service courtyard.

[4][5] The facade's slight concavity follows the square's circular shape, balanced by a convex granite staircase leading to a paved plaza in Rapolano travertine.

The facade on Via Roma includes a service entrance arch and a small cross-shaped space paved with blue ceramic tiles.

The eastern end features a semicircular stairwell volume with increasing vertical windows and a perimeter wall with a gate to the rear courtyard.

The post office palace was initially seen as "a bold attempt at fascist-era art, blending classical elements with a well-understood modernity"[8] and celebrated for its use of fine marbles.

In the context of a broader reevaluation of Angiolo Mazzoni's architectural work over the past years, the building is recognized as an example of "heavy yet evocative monumentalism", possessing "a vaguely sinister metaphysical allure".

[9] According to Quattrocchi (2006), the building "redeems itself from the heavy monumentalism of the exterior through the beautiful and functional interiors, which find a remarkable and evocative spatial wisdom in the episode of the helical staircase occupying the tower", adding that this differentiation between exterior and interior takes on "the sense of a transition from a casual yet predictable historicism to a more streamlined and internationally 'modern' language".