The term TYPE OF MAIL can refer to three different types of mail: FAN (3 letters), CHAIN (5 letters), and METERED (7 letters). FAN stands for First-Class Automation Network, which is a type of mail that is sent through the United States Postal Service. CHAIN stands for Commercial and High-Volume Account Network, which is a type of mail that is sent in bulk by businesses. METERED stands for Metered Mail, which is a type of mail that is sent with postage that is paid for with a postage meter.