This industry comprises establishments primarily engaged in providing mail services under a universal service obligation. Mail services include the carriage of letters, printed matter, or mailable packages, including acceptance, collection, processing, and delivery. Due to the infrastructure requirements of providing mail service under a universal service obligation, postal service establishments often provide parcel and express delivery services in addition to the mail service. Establishments primarily engaged in performing one or more parts of the basic mail service, such as sorting, routing and/or delivery (except bulk transportation of mail) are included in this industry.