39 C.F.R. § 959.4

Final demands for payment of postage will be accompanied by a copy of these rules and will:

(a) State that the demand is final unless appealed under these rules within 15 days after receipt of the demand;

(b) Describe the transaction on which the demand is based and the provisions of law or regulation alleged to have been violated; and

(c) State the manner in which the amount of the demand is computed.