HONOLULU — A former Hawaii publisher is set to auction what is believed to be one of three known surviving historic envelopes postmarked on the first day of the Pony Express.

The envelope is among 63 items that are owned by 88-year-old Thurston Twigg-Smith. He is the former publisher of The Honolulu Advertiser.
Robert A. Siegel Auction Galleries in New York will conduct the auction. The auction house estimates the collection’s value is $2.5 million or more.
The envelope is postmarked on April 3, 1860, and is valued at $300,000.
Twigg-Smith also will auction one of two surviving Pony Express letters that originated in Hawaii. It is valued at $500,000.
The Pony Express lasted 19 months, shuttling mail 1,900 miles from St. Joseph, Mo., to San Francisco.