Something for the postman to deliver working for the post office overseas? (6)

I believe the answer is:

packet

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If this is the answer I cannot explain how the clue works.

(Other definitions for packet that I've seen before include "Boat; paper container" , "Mail ship" , "bomb" , "Small parcel" , "Boat carrying mail" .)

I've seen this clue in the Irish Times (Crosaire) and the Irish Times.

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