Unfrei is a term used in the German postal system. If something is sent unfrei it means that the recipient pays for the postage.
This is often indicated on the envelope as “Gebühr bezahlt Empfänger”. Some companies pre-print their envelopes with “Bitte freimachen, falls Briefmarke zur Hand” requesting that you put a stamp on the envelope, but that they will pay the postage anyway if you do not.
To hear a simple explanation and a short discussion in German, listen to the podcast:
(Press the “play” button to listen to the podcast)
