Ray Johnson (1927-1995) was an American artist who played a key role in neo-dada, pop-art, and performance art movements. Johnson was the founder of what's known as "mail art." Mail art became a big thing in the 1950s. The artform combines whatever is being sent in the mail and the exchange between two or more people. The mail becomes art only once it's been dispatched. Mail art can consist of anything from drawings to stamps to collage. It doesn;t matter what the medium is, as long as it's circulated through the postal service.
The mail art that Ray Johnson sent to others can be seen here on his website, as well as the mail art that others sent to him. Although all of Johnson's mail art pieces stand on their own as experimental drawings in my opinion, I love knowing that these were all exchanges between him and others. Mail art is such an awesome way to connect with others, and I recommend that everyone tries it at least one time. Once you start, you may never want to stop.
"[Mail art] is a way to convey a message or a kind of idea to someone which is not verbal; it is not a confrontation of two people. It's an object which is opened in privacy, probably, and the message is looked at … You look at the object and, depending on your degree of interest, it very directly gets across to you what is there …" — Ray Johnson (Mail Art – Printed Matter)