Police are warning local businesses to be on their guard, almost a week after two suspicious packages were found at the Post Office.
Officers were called in by Isle of Man Post last Friday.
The packages were addressed to financial companies on the Island and were opened under controlled conditions in a joint operation with the Fire and Rescue Service.
Police say both items came from Algeria and they are now trying to find out who sent them and identify a substance inside.
Nobody who dealt with the packages has shown any ill effects but officers are advising vigilance and caution, especially in relation to mail from the North African country.
They are telling anyone who receives a similar package not to open or handle it unnecessarily.
The recommended procedure is to seal it inside an airtight container and dial 999.
Anybody who has handled such a package should wash their hands and any other exposed skin thoroughly.