Finland Mystery Postmark Solved - It's An Rpo

Well, it's a mystery to me, at any rate. I noticed this postmark on a stamp recently found in a purchased collection. On examining my own Scandinavian material, I found another copy with apparently the same postmark and a good possible for a third with a small portion of the inscription. Finding so many in a very small sample would indicate that it is quite a common postmark.

These were all on the same stamp and appeared to be from the same period though I could not decipher an exact date on any of them. What interested me was the word "expedition" which seemed to be the use of an English word on a Finnish stamp. The part I can make out is all in Capital Letters and spells "POSTKUPEEXPEDITION"

I am guessing that this word has some meaning which refers to how the mail was sent, but I would appreciate hearing from anyone that can give me an answer or point me toward a reference that I can use.

Hi backroads, there was a previous thread regarding this. Have alook and see what you think.
https://goscf.com/t/11921
Bill

An excellent thread. I had expected a translation would indicate a specific postal usage. It now gets moved to my international examples of Railway, Ship, Bus, etc. postal markings.

I believe that my title should be edited, if I can remember how, to give a link to the RPO topic.