Postage
From Memory Alpha, the free Star Trek reference
Postage was a fee levied by a mail delivery agency for use of their services. This money was typically paid prior to delivery of the parcel.
On Sigma Iotia II, Bela Okmyx once returned a letter from one of the residents of his territory with "postage due," indicating that he had not paid to send the letter back. (TOS: "A Piece of the Action")
