Postage due cover from Hong Kong

New express FDC from Hong Kong. This cover has a special machine postal cancellation on its back, the green one. This cancellation use to see in domestic prompt letter and it was my first one from overseas letter. Thanks Edward for sending me this interesting cover.

A friend sent me this cover affixed Taiwan stamp from Hong Hong then it arrived to Taiwan with a "T 240/230" mark. When I went to post office to get this cover, post office's staff did not ask me to pay the postage due. It's not very often to see this mark on my letters. So, I insisted to pay the postage due not only because I want to collect this unusual cover, but also I am a honest person. After some work, finally got this cover with correct postage due stamps on it.