Parcels sent abroad are subject to foreign customs inspection, which is basically in the form of random checks.
If customs consider your parcel to be special (e.g. large, too heavy or containing sensitive goods), they will generally take the initiative to contact the recipient to provide an invoice or clearance documents.
The cost of returning or destroying the parcel due to failure to contact the recipient or the recipient not cooperating with the initiative to contact Customs for clearance will be borne by the recipient.