I think this is the most difficult mail experiment I have carried out so far. I wanted to send this message to Heleen (the Netherlands).
I draw it it in the back of four similar envelopes:
So I obtained these (front):
I sent one of them from Morocco and then the second one from Spain. As I wanted every envelope arriving from a different country, I ask two friends for help (don't worry: I paid them in kind. In postcards, to be precise). So Laura sent the third envelope from the UK and Micu sent the last one from Hungary. So... five postal services involved in the matter!
I am not sure if I am going to repeat this. I was too anxious waiting for the four letters to arrive! But finally they did safe and sound. Here you can see two of them (from Spain and Morocco):