On May 3, 1978, Gary Thuerk, a marketer with the Digital Equipment Corporation, sent the very first spam e-mail to 393 Arpanet users. You can read the actual e-mail and its consequences at the link.
The first e-mail started more or less round 1965. The first spam came in 1978? That long? Wow. Marketers today are faster to utilize new technology for advertising.