There are myriad ways to send a message: You can text, DM, email, or send good old-fashioned snail mail. Another mode to add to the mix? Dive and drop a letter via sea mail at Susami’s underwater mailbox.

A small fishing town in Wakayama Prefecture, Japan, Susami is home to about 3,700 people, water views, and one of the world’s few under-the-sea mailboxes. Here, visitors place postcards in a red mailbox where they get collected and then sent off to recipients, just like traditional mail. The biggest difference is that this mailbox is located about 33 feet below the surface. 

This is how it works: Interested mail senders purchase water-resistant postcards at a local dive shop and use oil-based markers to write a smudge-proof message. They then dive underwater to put their notes in the mailbox. Every day, Kenji Nakanishi, who runs the shop and manages the postbox, dives to collect the cards and takes them to the local post office, where the notes are sent to their recipients. Like the idea, but not down for diving? You can still purchase a note and ask a diver to send it on your behalf, according to reviews on Tripadvisor.

According to The Japan Times, the idea came to be thanks to Toshihiko Matsumoto, the town’s then-70-year-old postmaster. In 1999, Matsumoto proposed the underwater mailbox as a way to attract more tourists and divers to Susami. 


“I thought it would be interesting if divers could send letters from under the sea,” Mastumoto, who worked for the post office for about 40 years, said in a video by Great Big Story. “I thought it would be good for the post office and good for tourism.”  

Not only was the idea innovative, it was also record-making. The red letter collector went on to be recognized by Guinness World Records as the world’s deepest underwater postbox, and as word got out, more divers came to see it for themselves.

Between 1,000 and 1,500 pieces of mail are collected annually, and as of 2018, nearly 38,000 letters had been sent. 

“I think the underwater mailbox has been a real asset for tourism in Susami,” said Nakanishi. 

Underwater mailbox in Vanuatu

Furthermore, it’s now among a network of other underwater mailboxes on the sea mail scene. For example, in 2003, Vanuatu launched the Underwater Post Office, where divers can send off waterproof postcards that have been embossed with the help of postal workers stationed on the seafloor. And in 2015, Malaysia unveiled its underwater mailbox located 131 feet below sea level, breaking records as the deepest underwater mailbox in the world.


While the underwater aspect is more novelty than necessity, it is nevertheless delightful. As YK, one of the visiting divers to Susami, said in a Youtube video, “So, obviously having a mailbox under the sea is sort of completely useless, but at the same time I loved my experience there because it was something new and interesting for me.” 

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