About a thousand stolen letters were recovered during an eviction at Toongabbie in March.
Holroyd police crime manager Chris Weidemann told the Sun police found about 700 to 1000 letters addressed to different addresses during a routine eviction recovery of the property on Wednesday, March 26.
The occupant was not present for the eviction and has not been located since.
"Several hundred of the letters had been opened but a substantial quantity of them have not been opened," Detective Inspector Weidemann said.
"The officer who wrote the report has been checking whether there have been any identification documents, particularly with the mail items that have been opened."
Possession of stolen mail goods is a specific offence, and another relevant offence is the possession of identity documents with intent to commit fraud.
"A lot of mail theft is fraud related, with stolen identification documents used to commit fraudulent offences," Detective Inspector Weidemann said.
Detective Inspector Weidemann said it appeared the mail items came from private letterboxes across a wide area around Toongabbie, rather than being stolen from Australia Post.
"We're working with Australia Post to have those items returned to their rightful owners," he said.
In early March, Holroyd police issued a general warning to Sun readers to guard against mail theft due to continuing incidents in the region.
In January, Hills police charged a 38-year-old man of no fixed address with stealing more than 200 documents from houses in Castle Hill, Baulkham Hills, Kenthurst and Lane Cove.