The extraordinary admission was made in a letter written in response to a Freedom of Information (FOI) request lodged by ABC News.
The request sought details of any investigations into illegal drugs being sent through the post.
"Australia Post has an obligation to inform relevant authorities should it suspect the presence of illegal goods in mail items, but lacks the technology or equipment to detect [such goods]," the letter said.
"Australia Post does not have, for example, sniffer dogs, X-ray machines or explosive trace detectors."
"Australia Post lacks legal authority to open mail."
The online market for illegal drugs largely relies on postal services like Australia Post to deliver purchases.
In a statement to the ABC, Australia Post said funding was not the reason behind the lack of technology to detect illegal goods and that it was not in a position to change any laws.
"Australia Post does not seek this legal authority which, in Australia Post's view, properly sits with law enforcement agencies," the statement said.
Do you believe them?
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