History
The invention of spam
On 3 May 1978 a sales representative sent an invitation to 393 recipients on the ARPANET. It worked. That is precisely the problem we have been living with ever since.
The invitation
Gary Thuerk worked in marketing at the Digital Equipment Corporation and wanted to present new machine models. Rather than telephone people one by one, he sent an invitation to demonstrations to practically every ARPANET participant on the West Coast whose address appeared in the directory of the day.
The reactions were largely hostile — complaints followed, and a reprimand from the network administration, which took the view that the network was not intended for commercial advertising. Thuerk himself later reported that the exercise led to considerable sales.
Put the two together and you have the arithmetic that explains the rest of the story: the annoyance landed on the recipients, the revenue on the sender. That asymmetry is not the consequence of bad manners; it is built into the shape of the system.
Why sending costs nothing
With every older means of communication the sender carries the cost. A letter costs postage, a call costs charges, a newspaper advertisement costs by the column inch. Those costs limit unwanted approaches more effectively than any prohibition: scattering pays only if the hit rate carries it.
With email that brake is gone. Delivering to one more recipient costs practically nothing, and what it does cost — processing time, bandwidth, storage — is borne mostly by those receiving. Which makes bulk sending worthwhile even at a hit rate close to zero.
Where the word comes from
The term does not come from technology but from a 1970 sketch by the British comedy group Monty Python. In it, every dish on a café's menu contains the tinned meat brand Spam, while a group at the next table sings the name until no conversation is possible any more.
Exactly that image — the problem is not the content, it is that the content drowns out everything else — was taken up by network users two decades later for repeated, unwanted messages. So from the very beginning the term describes not malice but quantity.
The consequence for everyone else
The real effect of spam lies not in the messages you throw away but in what it made of the system. Because unwanted mail could not be limited at the source, the decision moved to the recipient — and ever since, recipients decide not merely about the individual message but about the sender.
That is how today's situation came about: anyone sending a message has to prove they are allowed to (sender authorisations and signatures), and even then the reputation of where it came from decides whether it arrives. A small, correctly configured sender therefore has a harder time than a large one with a well-kept name — even though the protocol treats them identically.
That is the legacy of 1978: a system that presupposed trust had to learn, after the fact, to organise mistrust. It has learned that astonishingly well — but the price is that taking part now costs an effort nobody would have had to explain before the first bulk mail.