Express couriers and air freight
Anything not sent by mail needs a formal or informal entry (91 FR 37789). Up to $2,500 it can be informal, mainly Entry Type 11; above that, formal entry generally applies.
The courier or the line's broker files the entry and pays CBP. Then it either bills you (duties unpaid, DDU) or has already charged you in the shipping price (duties paid, DDP). An automated informal entry carries CBP's $2.77 merchandise processing fee (CBP User Fee Table). A courier's brokerage fee is the courier's own charge, not a government one.