An 1844 cover displaying stamps from three independent US mail handlers sold for $28,000 at Robert A Siegel.
The lot led the May 4 sale of the Dr Carmen A Puliafito Collection of US Independent Mails in New York.
Included on the cover is a 5c American Letter Mail co, two Pomeroy's Letter Express 5cs, and three Letter Express 5cs (one single and a pair).
The letter was sent from hardware manufacturer W Bingham & Co in Cleveland to Pierpoint & Hotchkiss in Connecticut - a distance of over 500 miles.
Independent mailers often acted in relay to send post over long distances and offered lower rates than the official Post Office.
Siegel states the lot is "universally acknowledged to be the most valuable and important cover of the independent mail era."
It explains: "Considering that the first United States Postmasters' Provisionals would not be issued until nearly one year after this was mailed, and the first General Issue two years after that, the presence of six stamps in three colors from three different stamp-issuing entities on this letter must have been perceived as extraordinary, even in 1844 when it was delivered to Pierpont & Hotchkiss.
"Today, it is one of the undisputed icons of American postal history."
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