Small-scale art whose senders used the U.S. Mail for distribution, it consists of envelopes that are drawn or painted on or contain collages or the like, on which there may be "artistamps" (stamps designed by an artist and not valid for postage) or rubber-stamping. Participants in mail-art networks generally accept the unwritten rule that mail art is freely exchanged and if shown in exhibitions, the exhibitions are non-juried and open to everyone. Works are generally not returned to the artist. Mail artists include Eleanor Antin, On Kawara, Yoko Ono, Sarah Jackson, and Tom Marioni, who sent mail-art announcing his fictitious 1973 appointment as Director of the San Francisco Museum of Modern Art. Sources: Daniel C. Boyer, Artist; Robert Atkins, "Art Speak"