The article describes the most common reasons for returning parcels from abroad to senders:

Delivery attempted, the addressee was not at the place of delivery.

Mailbox closed for non-payment of rent.

Used only when it is known that the addressee is deceased and mail cannot be delivered to another person. This endorsement must be made personally by a delivery employee and under no circumstances may be rubber-stamped. Mail addressed in care of another is marked to show which person is deceased.

Failure to comply with 508.1.8.1 through 508.1.8.3.

Address is not readable.

Mail returned to sender by order of General Counsel (or under 508.1.0 and 508.2.0) because of dispute about right to delivery of mail and it cannot be determined which disputing party has more rights to mail.
Address is missing a number, street, box number, route number, or geographical section of city or city and state omitted and correct address is not known.

Addressee has moved and filed no change-of-address order.

Addressee failed to provide a mailbox for receipt of mail.

Addressed to nonexistent number and correct number is not known.

Addressed to nonexistent Post Office.

Addressed to nonexistent street and the correct street is not known.
Mail undeliverable at address given; no change-of-address order on file; forwarding order expired. Addressed to location outside delivery limits of Post Office of address. Hold mail for out-of-bounds customers in general delivery for specified period unless addressee filed order. Hold mail for out-of-bounds customers general delivery for specified period unless addressee filed an application).

Addressee refused to accept mail or pay postage charges.

The post office is not intended to accept delivery.

The mail is without postage or indication that postage fell off.

Mail returned to sender under false representation order and lottery order.

Mail returned to sender under false representation order.

Mail returned to sender under lottery order.
Addressee is temporarily away and period for holding mail is expired.

Addressee abandoned or failed to call for mail.

House, apartment, office, or building not occupied. (Use only if mail addressed to "Occupant.").