Illustrated Envelopes and Cards

Recently I posted the cover of Jean-Michel Folon's Lettres a Giorgio, a collection of illustrated envelopes and postcards by the Belgian artist, all addressed to Giorgio Soavi in Milan, Italy, between 1967-1975. Above and below are examples of the contents of this book.
I love these colorful envelopes and cards! Imagine being the recipient of these treasures.

They are mailed from various countries: Italy, the USA, France, Japan. I like seeing not only the quirky, clever illustrations, but also the postmarks and the stamps. (In the above example, postage from the States to Europe was 20 cents. Now it is 90 cents.)