1 Letter-size Basics 1-1 Types of Letter-size Mail In addition to determining the mail processing category using the weight and shape of the mailpiece, the Postal Service also classifies mailpieces by the way they are prepared. The Postal Service bases these classifications on how efficiently Postal Service equipment can process your mailpieces, which fall under one of the following three categories: “Automation” letter-size mailpieces are machinable and contain correct delivery point information in the imprinted Intelligent Mail barcodes. Letters and cards can receive postage discounts if they meet automation standards. “Machinable” mailpieces can be sorted on Postal Service processing equipment. Sorting mail on automated equipment is more efficient than manual processing, so properly prepared machinable pieces can qualify for lower prices — but not for Automation prices because achinable pieces do not have a qualifying barcode. “Nonmachinable” mailpieces cannot be processed by Postal Service equipment. Because nonmachinable pieces must be sorted manually, higher postage prices might apply because of the additional postal handling needed.