These are organized by form and function.
These are organized by a classification scheme developed exclusively for Cosma. More…
mail : material sent or carried in the postal system — Webster
post : an organization for handling mail — Webster
Mail or post, is a system for transporting letters and other tangible objects: written documents, typically enclosed in envelopes, and also small packages are delivered to destinations around the world. Anything sent through the postal system is called mail or post. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century national postal systems have generally been established as government monopolies with a fee on the article prepaid. — Wikipedia