Mail art (also known as Postal art and Correspondence art) is a populist artistic movement centered around sending small scale works through the postal service. It initially developed out of the Fluxus movement in the 1950s and 60s, though it has since developed into a global movement that continues to the present.
Media commonly used in mail art include postcards, paper, a collage of found or recycled images and objects, rubber stamps, artist-created stamps (called artistamps), and paint, but can also include music, sound art, poetry, or anything that can be put in an envelope and sent via post. Mail art is considered art once it is dispatched. Mail artists regularly call for thematic or topical mail art for use in (often unjuried) exhibition.
The mail artist community values the interconnectedness of the participants and promotes an egalitarian ethos that frequently circumvents official art distribution and approval systems such as the art market, museums, and galleries. Mail artists rely on their network as the primary way of sharing their work, rather than being dependent on the ability to locate and secure exhibition space. The community embraces this outsider or alternative status, and refers to itself as “The Eternal Network” or just “The Network.” At its core, mail art is about interpersonal communication, exchange and the creation of a virtual community of participants. In this way, mail art can be seen as anticipating the cyber communities founded on the Internet.
Thank-you to Wikipedia for this great description of Mail Art!