The find has stunned Margaret Street, Tighes Hill, retiree Tom Hickmott, who picked it out of the letterbox with the rest of his mail.

"It's just this brown paper envelope with the address - the Intercity Company, Port Washington, New York - printed or stamped in ink," Mr Hickmott said.

"The sender details are written in this beautiful handwriting - 8 Margaret Street, Tighes Hill, Newcastle - but the sender's name has been rubbed out.

"It was sent by registered mail - number 947 - from Tighes Hill post office on October 12, 1938.

"It got to New York on November 4, 1938, then it ended up back here, sent to me with a new 'return to sender' sticker on it and a Port Washington, New York stamp dated May 15, 2010.

"Where it's been in the meantime, and who sent it, I don't know."

Mr Hickmott said the envelope was empty and had been stuck down again with sticky tape.

"Whatever was in it is long gone," he said.

Mr Hickmott moved to the Margaret Street house in 1967.

"The people who we bought it from were called O'Sullivan, a mother with a son who was a doctor, but I don't think they were there in 1938," Mr Hickmott said.

Postage on the letter was paid by two green fourpenny "koala" stamps, and Mr Hickmott said the registered mail number 947 made sense because the post office had only opened the year before.

"The post office building down the bottom of Elizabeth Street is apartments now, but the date 1937 is on the front wall," Mr Hickmott said.

"It's probably some sort of a record . . . for a letter to take so long. Hopefully the publicity will help us find who sent it."