From Pink Tentacle:
Residents of the coastal town of Susami in Wakayama prefecture love the sea and the post office so much that the town once installed a mailbox on the ocean floor for scuba divers. Now, further evidence of this powerful sea/mail love comes in the form of “Surumail” — edible postcards made from squid.
Produced by the Susami fishing cooperative, Surumail postcards consist of dried surume squid (Todarodes pacificus), the local seafood specialty. The squid jerky is flattened and vacuum-packed into the shape of a postcard, and an adhesive label is included for the postage, delivery address and a short message.