Post Office Mauritius
Again as a result of an error in postal stamps. In September 1847, while inviting friends and celebrities to a ball the Mauritius Post Office issued a set of stamps but the words of "Post Office" instead of "Post Paid" were engraved on the copper plate of the stamp. This ended up being a big mistake as 240 copies were sent before noticing the error. Only 26pieces remain today in the Post Office of Mauritius.
Estimated Price : $1.67 million