Spam exploded in 2003[1] to the modern experience of it. Before that, spam was somewhat infrequent, even without countermeasures.
I recall in the 2001 time period being so annoyed by each individual spam note that I would respond to the appropriate "abuse@" email. By 2004, it was a torrent and totally impractical, and I don't think it was because of my own notes to administrators.
I remember the first spam I ever received. It was in 1998 on my first day working at AOL. It promised an advanced degree from a prestigious, unaccredited institution. The spammers were somewhat honest back then.
I recall in the 2001 time period being so annoyed by each individual spam note that I would respond to the appropriate "abuse@" email. By 2004, it was a torrent and totally impractical, and I don't think it was because of my own notes to administrators.
[1] https://www.emailtray.com/blog/email-spam-trends-2001-2012/