A relative who is no longer living told me that when her uncle (Jewish, living in hiding in France) was discovered and put on a train transport to Auschwitz, not long before liberation, he threw a note to his sister out of the train to let her know his fate, and this note was miraculously delivered to his sister in London.
How might this note have reached its destination?
I'm trying to picture this, step by step. He would likely have been in a windowless cattle car -- so how did he get a note out of the train? Whom might he have given it to? Would this have been from the station where he was first put on the train, or farther along the route? Would the note then have been sent through the postal service, or by some other means?
Edit: I imagine the uncle and his wife would have been killed upon arriving, or shortly after arriving, in Auschwitz. The officially-encouraged-postcard hypothesis seems unlikely to me, partly from the way the story was told to me, and partly because my impression is that towards the end of the war, Germany was hanging by a thread and would not have bothered with this type of PR any more.
The way this family history was explained to me, it was a note thrown out of the train, and it was considered remarkable that the note reached his sister.