This story and its variants made the rounds back in the 1960s.
It was very late at night one evening. A fully uniformed mailman with a mailbag was seen walking down Queen's Road in the same manner as any postal carrier would in the middle of the day away from the former Wanchai post office.
His body language did not suggest he was off duty, relaxed, and now on the way home. No, carrying his mailbag, he walked down the street with the professional determination of one who has a job to do.
To see a mailman on duty so late at night was odd enough; this wouldn't be, however, the strangest aspect of the story. The most bizarre details were yet to come.
Some who passed by him on the street stated the mailman was devoid of facial features; others said his eyes emitted light.
Those who received mail late that night opened the ordinary appearing and properly addressed envelopes only to find, according to some sources, either a blank sheet of folded paper or a bill of paper money. It is said that most of these recipients of the letters regarded all this as some kind of prank.
Sadly, those who passed by him and saw his face and those who received letters from him would all have something in common--each individual would pass away within three days.
When news of this became known, it caused many, of course, to be greatly afraid. So, some unnamed residents contracted the services of a ghost catcher or exorcist from nearby Hung Shing Temple [洪聖廟] in Wanchai. The powers of the spirit that had manifested itself as a mail carrier were admittedly very formidable, and the holy man charged with ridding Hong Kong of this specter was unable to extinguish the menace completely. However, in the end, the exorcist succeeded in at least keeping the spirit at bay in some kind of limbo, thus making it unable to continue its rounds as long as he, the holy man, lived.
In time, the holy man passed away, and his son took his place in making sure the threat posed by the deadly being remained neutralized. According to one version, the son of the holy man said to the spirit, "Until the day I die, you shall not return to plague this area!"
At the time this is being written, the son of the holy man is still said to be alive, and so the frightful presence remains inactive . . . for now . . .
Fan Qicong & Shi Zhiming. Xianggong Dushi Chuanshuo Da Baike 香港都市傳說大百科 [The Big Encyclopedia of Hong Kong Urban Legends], Chunghwa Book Company, 2021, pp. 76-82.都市传说香港鬼邮差 - Google Search
Fan Qicong and Shi Zhiming suggest that the ghostly mail carrier might be a modern manifestation of a being from ancient Chinese mythology, the ghost courier, or psychopomp, that escorts the dead to the underworld. They specifically cite Ox-Head [牛頭] and Horse-Face [馬面], two of the most famous examples of such couriers as possible inspirations.
Motifs: F159.4, "Demon guide on otherworld journey"; M341, "Death prophesized."