Publishers must maintain a Known Office of Publication (KOP) at the location where the original entry Post Office™ for Periodicals mailing privileges is authorized. The KOP is a public office where normal business of the publication is conducted during normal posted business hours. This must be a domestic physical address and cannot be a post office box. Publishers must keep circulation records of the publication at the KOP or make them available upon request at that office for review by Postal Service personnel.
