Somewhere I may still have a 25(?) page 1974(?) published directory of all known email addresses on the ARPAnet. As I recall the addresses were centrally assigned to be a minimal number of characters because many people were still using ASR33 teletypes. I was something like RMM5@BBN.

SPAM as a term existed on usenet at least in the early 80s for a posting that was crossposted to many inappropriate newsgroups. And as I recall some of this spam was blatant comercial advertising.