Honoria answers: Each mail artist is her own Rosetta stone using her participation to decipher the network. Even if scholars and other participants write studies and histories of the mail art network, mail artists themselves understand the whole network through the shifting and responsive contents that flow through their own mail boxes. So every mail artist has a different body of mail art.
The Internet made it much easier to find mail artists' personal narratives that used to be distributed only in small zines with limited circulation. An Internet search for mail art will find some artist's personal narratives in writing, but the Internet has also encouraged more posting of pictures. It is a more natural medium for many mail artists to make artworks than it is to write, so the graphic environment of the Internet is attractive to mail artists. The zines were usually xeroxed in black and white. Because of their capacity to publish images was limited to grainy greyscale illustrations the zines tended to feature interviews with mail artists together with contact addresses. If a zine reader wanted to continue a discussion with the artist in the zine you sent your own art or letters directly to the artist; then you received original art from the artist in the zine. The conversations in the zines and the rich physical information in the mail box were each mail artist's clues to the nature of the whole network.