This article aims to show that so-called Mail Art (art distributed via theinternational postal system) is based on five paradoxes. These paradoxes, which correlateto how Mail Art is distributed and exhibited by means of changing technologies,its aesthetics, its democratic ideals, and its transnational character, explain howMail Art has emerged and been constructed as an artistic medium on the stage ofworld cultures. While the paradoxes of Mail Art are specific for this particular medium,I argue that all media types are more or less marked by inherent paradoxes. Thefact that Mail Art includes all kinds of material, sensorial, spatiotemporal, and semioticmodes makes it an unusual art form, but here it is primarily meant to be an exampleof the ambiguous ways in which media types in general are delimited and defined.