What is the main difference between First-Class Mail letters and First-Class Package Service?

• A. The service distinctions are based on item shape
• B. First-Class Mail letters are delivered with guaranteed overnight service
• C. First-Class Package Service handles only international shipments
• D. Letters are for flat items; First-Class Package Service is for small, heavier parcels

Answer: (D)

The main concept is that USPS separates First-Class mail by item type: flat versus non-flat. A letter is a flat item that fits in a standard envelope and is priced and handled as a First-Class Mail Letter. First-Class Package Service covers small, heavier items that aren’t flat—parcels or packages that need a box or padded envelope. Because of this difference in item format, letters stay within the letter pricing and handling, while packages use the package service for small, heavier items. The other statements don’t fit this distinction (overnight delivery isn’t guaranteed for First-Class, and this service isn’t limited to international shipments).