Intended to attract more visiting divers to what is already claimed to be a popular diving area, the postbox is set at a depth of 11m.

It has been been made in the form of a 1.8m-high white Coleman’s pygmy seahorse, a species that was discovered at the site in 2007.

Ahmed Gabr, the Egyptian diver who holds the Guinness World Record for deepest scuba dive in salt water, attended the ceremonial unveiling of the receptacle, with a local dignitary joining him to dispatch the first postcard.

A souvenir-shop owner had already installed a postbox at a depth of 13m off Green Island two years ago, but because it was unauthorised it was later removed.

The idea of underwater postboxes is not a new one.

In 2002 the otherwise undistinguished fishing port of Susami in southern Japan set a Guinness World Record for its 10m-deep postbox.

Since then it has been said to collect as many as 1500 items of mail a year, with divers writing and depositing water-resistant postcards that are later collected and posted by the local dive-centre.

Taiwan installed its first underwater postbox in Magong City last year, but it attracted less attention as it was set at a depth of 6m.

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