Mailing Standards of the United States Postal Service, International Mail Manual> 7 Treatment of Inbound Mail > 760 Forwarding > 766 Retention Period
Post Office facilities must hold international mail items for pickup by the addressee for 30 days. However, inbound Express Mail Service items must be returned to sender after 5 days, unless the sender specifies fewer days on the piece.
An item refused or known to be neither deliverable nor forwardable must be treated as undeliverable immediately.
Items enclosed with a sender’s request for return within a specified period may be held for the period specified, not to exceed 60 days.
An item conditionally refused by the addressee because of the duty assessed (see 713.233 for the procedure when the addressee asks that the U.S. Customs Service reconsider the duty) is held until the customs office gives a decision on the protest. If no decision is reached within 30 days, the customs office should be asked to expedite its decision.
An item returned from customs custody with advice that the addressee has not complied with required customs entry procedures must be treated immediately as undeliverable.
An item bearing the sender’s request for delivery to an alternate addressee must be held 15 days at the disposal of the first addressee and 15 days at the disposal of the second. If the alternate addressee is at another Post Office facility, the item is forwarded subject to 764.1, and the 15–day period begins from the day of receipt at the second office of address.