Sharp edged or pointed items. The full list of items not accepted for the mail is covered in the IATA regulations covering dangerous goods. Your local Post Shop is always happy to help but, due to the complex nature of some products, it remains the senders responsibility to check these regulations to see if the product can be sent by post. All items, irrespective of packaging, listed in the IATA regulations are not to be sent through the post. The regulations can also be purchased from selected bookstores.
Many overseas countries have additional restrictions and prohibitions on the contents of mail.