I was hesitating about sending this postcard to Heleen (the Netherlands), not sure if postal machines would be able to read the address and find the stamp on the front side of the postcard... But it eventually arrived.
And the same week, John (the UK) had a similar idea. Not the address, but he wrote the message on the front side, in the form of an old telegram:
Actually, the postcard is a reproduction of a greeting telegram for Valentines Day (Rex Whistler, 1936), from the British Postal Museum & Archive.