You're been sent this postcard because an Amateur Radio operator near you has received a Radiogram which was addressed to you.
A Radiogram is like a telegram, except that it is handled solely by licensed Amateur Radio operators, free of charge. The message on the other side of this postcard had been relayed entirely by radio from one city to another, rather than being sent by email or telephone. This is a confirmation of that message.
Amateur Radio ("ham") operators stand ready to serve the public whenever regular communications systems, such as the Internet, become unavailable, especially during natural disasters. By handling Radiograms such as this one, "hams" are getting valuable practice in public service.
Learn more at www.arrl.org.