Most expensive franked letter

An 1847 letter to wine merchants in Bordeaux, franked with the 1d and 2d first issues of Mauritius was bought by an anonymous buyer in less than a minute for CHF6,123,750 ($4,075,165 / £2,811,639) at a sale conducted by Geneva-based auctioneer David Feldman (Ireland) at the Hotel International in Zürich, Switzerland on 3 November 1993.