Aioe.org tries to reject spam messages sent to newsgroups using cleanfeed, an old antispam software written in perl. It plots a nice html statistical page that is printed below. Everybody should consider that these data do not represent a reliable sample of the number of spam messages actually posted on usenet because they only refer to this server.
Filter started: Tue Jul 20 12:08:53 2021
Report generated: Fri Sep 17 12:30:01 2021
Uptime: 5098868 seconds
Accepted: 376999
Rejected: 70505
Refused: 83
Period since last report: 3600 seconds
Articles examined (this period): 0.2/s
Articles accepted (this period): 0.1/s
Articles examined (entire uptime): 0/s
Articles accepted (entire uptime): 0/s
MD5 entries: 300 Rejecting: 24
PHL entries: 535 Rejecting: 2
PHN entries: 362 Rejecting: 6
PHR entries: 0 Rejecting: 0
FSL entries: 432 Rejecting: 0
MID history: 257
Supersedes entries: 1