Required for new construction and major renovations, 4C horizontal mailboxes are ideal for commercial buildings, multi-family housing units, apartment complexes, government and military bases, schools, colleges and other residential and commercial developments. Salsbury Industries manufactures USPS STD-4C Horizontal mailboxes that are required for new construction and/or major renovations.  4C mailboxes are made of heavy duty aluminum and stainless steel hardware and come available in configurations that are 1 door wide (single column) and 2 doors wide (double column).