What is the maximum size of a letter according to postal regulations?

The maximum size of a letter according to postal regulations is indeed determined by specific dimensions that classify a piece of mail as a letter. The correct answer provides dimensions of 6 1/8 inches in height, 11 1/2 inches in length, and a thickness of 1/4 inch. This size adheres to the standards set by postal services, which define letters as a flat mail piece that can easily be processed and delivered in an efficient manner.

In this context, the chosen dimensions allow for automated processing while still being manageable for handling by postal workers and incorporating into standard delivery systems. Letters that exceed these dimensions may be classified as larger mail pieces or packages, which are subject to different postal rates and handling protocols. Thus, the specification of 6 1/8" x 11 1/2" x 1/4" ensures compliance with postal guidelines, contributing to the efficient sorting and delivery of mail.