With the exception of First-Class letter mail, each piece of outgoing U.S. mail should be identified with its service class. Examples of commonly used mail classes are listed below. Mail Services can provide labels for USPS premium mail classes. General classes can be handwritten, labeled, or printed on the piece. The words should be large and easy to read as noted below.

Domestic Mail Classes

EXPRESS MAIL (Address label available)
PRIORITY MAIL (Label available)
FIRST-CLASS
PARCEL POST
MEDIA MAIL
LIBRARY MAIL

Global Services

GLOBAL EXPRESS MAIL (EMS) (label available)
GLOBAL PRIORITY MAIL
GLOBAL AIRMAIL (Letter-Post and Parcel-Post)
GLOBAL ECONOMY (Letter-Post and Parcel-Post)