The fonds donated to MACBA was created by exchanging cards with different artists from around the world, following a call for presentations by Merz Mail and, above all, from Sousa’s correspondence with a smaller group of artists with whom he maintained a certain friendship and affinity, such as the South American creators Edgardo Antonio Vigo (Argentina), Clemente Padín (Uruguay) and Guillermo Deisler (Chile, at the time resident in Germany); the Americans John Held, Gerard Barbot, Jas W. Felter and Ray Johnson; and the Europeans Vittore Baroni, Guy Bleus and Ruud Janssen. The fonds contains diverse material from the Merz Mail archive related to mail art, including correspondence, postcards, envelopes, graphic material and objects belonging to Edgardo Antonio Vigo and Ray Johnson, among others, as well as publications and artist stamps. This collection contains digitalised works of mail art from his fonds.