It's been years since I've written about spam. That article was really focusing on the McColo shutdown.
Recently I came across a Quartz article that said that spam is at a 10-year low based on work by Symantec. This prompted me to revisit my spam tracking.
My numbers completely agree with Symantec's findings.
For background, the way I get my numbers is that every Monday I log into a Gmail account and note the number of e-mails in the Spam folder.