An internet search for Ray's name will find a lot of information about the beginnings of mail art as a network that rapidly expaned in the 1960s. To learn more you may want to join the group: rayjohnsonbunnyclub at yahoo
Ray Johnson memorial projects:
http://www.artpool.hu/Ray/RJ_memorial.html
A rich tour of correspondence work by Ray Johnson:
http://www.artpool.hu/Ray/raymap.html