39 C.F.R. § 262.6 – Retention and disposal.

(a) Records control schedule. A directive describing records series that are maintained by components of the Postal Service; it provides maintenance, retention, transfer, and disposal instructions for each series listed, and serves as the authority for Postal officials to implement such instructions.
(b) Disposal (records). The permanent removal of records or information from Postal Service custody; included are:
1. (1) Transfer to the National Archives.
2. (2) Donation to the Smithsonian Institution, local museums or historical societies.
3. (3) Sale as waste material.
4. (4) Discarding.
5. (5) Physical destruction.
(c) Retention period. The authorized length of time that a records series must be kept before its disposal, usually stated in terms of months or years, but sometimes expressed as contingent upon the occurrence of an event; usually the retention period refers to the period of time between the creation of a series and its authorized disposal date; however, in some cases it refers to the length of time between the cutoff point and the disposal date.