From “Run Your Own Mail Server” chapter 0:

“In 1978 Gary Thuerk, an employee of the Digital Equipment Corporation, emailed several hundred people he didn’t know an invitation to a demonstration of the new DEC packet-switching systems.  (…) Five days after the message went out the chief of the US Air Force’s ARPAnet Management Branch, Major Raymond Czahor, called Thuerk’s boss to tell them to never do it again on pain of disconnection.

This first advertising email sold twelve million dollars of computers.”