A collection of 63 historic Pony Express postmarked envelopes and stamps owned by retired Advertiser publisher Thurston Twigg-Smith sold for $4 million today in a New York auction.

The auction was conducted by Robert A. Siegel Auction Galleries in New York City. The pre-sale estimate was $2.5 million.

The only known Pony Express-originated letter addressed to Switzerland and one of only two known surviving Pony Express letters that originated from Hawaii sold for $632,500 each.

“The Hawaiian Pony Express cover ... has a rare $4 denomination Wells Fargo Pony Express stamp and it carried documents from the U.S. Consulate in Oahu, Hawaii to the U.S. Treasury Department in Washington, DC. in August 1861,” said Scott R. Trepel, President of Siegel Auction Galleries.

Another of the collection’s highlights is the finest of only three known surviving stamped covers postmarked on the first day of the Pony Express service, April 3, 1860. It sold for $460,000.

Twigg-Smith, 88, is a descendant of Hawaii missionaries. He began collecting stamps at the age of 8 in 1929. He was Advertiser publisher from 1961 to 1993.