There is a post office in the world that is completely underwater and from here you can send water-proof postage to the whole world.
This post office is located near a small country of southern Naval vicinity located on Vanuatu beaches, which was inaugurated in 2003 and it is still working, but it is not very deep and it is barely 10 feet or 3 meters deep. One of the 80 islands present here is near the Highland Islands.
Scary and scuba diving in such a way can easily reach. You can buy a water-proof postcard from the post-drained post office and send them a ticket and send them anywhere around the world. If no staff is present in the post office, you can put your postcard in the nearest postal box (drop box). The clerk in the Vanuatu Post Office puts a special seal instead of ink so that there is a further proof of the process. The dropdown of the box is often filled with seafood and you have to work hard for it. After 24 hours, the postal staffs vacuum it, but first make sure you have purchased water-proof postage from the island.