Which category is NOT a type of mail processing category?

The category known as oversized packages refers specifically to larger items that do not fit within standard size limits for regular mail services, and it does not represent a classification that postal services typically use for processing mail. Mail processing categories are usually defined by size, shape, and service type, and common categories include letters, parcels, irregular parcels, and nonmachinable items. Each of these classifications has distinct guidelines and processing requirements.

In contrast, letters are defined by their smaller dimensions and are processed through letter sorting systems. Irregular parcels are classified based on their unique shapes and characteristics that prevent them from being standardized, while nonmachinable parcels are those that cannot be handled by automated machines due to their size or other factors. By understanding these distinctions, it becomes clear that oversized packages do not fit within the established categories for processing, making it the correct choice in this context.