E-mail began to develop in 1965 when a messaging system to allow users of a shared mainframe to communicate locally created. It wasn't until 1971 that Ray Tomlinson picked the @ symbol addressing convention to allow inter-networked machines to exchange messages. Oh and if you're wondering what the first e-mail he sent contained, he believes it was something along the lines of "QWERTYUIOP" but he can't quite remember. Perhaps because he couldn't check his sent items as it wasn't until 1972 when the first e-mail management program emerged. No wonder so many people in the sixties shared peace and love since they didn't have to deal with spam.
In the seventies e-mail was used primarily be researchers and government agencies. Although believe it or not, the Queen of England did send an e-mail in 1976 as part of a demonstration and was the first head of state to do so! At this time spam didn't exist unless you were referring to Spam of the meat variety. It was quite impressive then that in 1975, Dr. Jon Postel wrote the IETF document RFC706 related to the possibility of junk e-mail titled "On the junk mail problem" but figured it would be the result of a malfunctioning machine:
It would be useful for a Host to be able to decline messages from sources it believes are misbehaving or are simply annoying. If the Host/IMP interface protocol allowed the Host to say to the IMP "refuse messages from Host X", the IMPs could discard the unwanted messages at their earliest opportunity returning a "refused" notice to the offending Host.
He also went out to suggest black listing based on a frequency analysis of messages from a host:
A Host might make use of such a facility by measuring, per source, the number of undesired messages per unit time, if this measure exceeds a threshold then the Host could issue the "refuse messages from Host X" message to the IMP.
The first spam message didn't really appear until 1978 when the DEC marketing department sent a message advertising a seminar in California. In 1988, a person posted to multiple newsgroups asking for college fund donations. The term "spam" emerged in 1993 when usenet moderation software with a bug posted around 200 messages by accident. From 1994 onwards the spam problem continued to escalate to the situation we have here today where open relays and proxies were dropped in favor of compromised home user machines.