Photostat of Zimmermann Telegram, as received by the German Ambassador to Mexico, January 19, 1917
The idea that Germany was proposing to give away a chunk of the United States to Mexico was so outlandish, many people doubted the telegram's authenticity. This copy, obtained by the State Department from Western Union, and the decode of the message, served to authenticate the Zimmermann Telegram.
National Archives, General Records of the Department of State