And a large portion of those spam are malicious scams. Mail that say "confidential" , "open immediately" in red ink, fake credit cards, fake checks ect.
When I was a residence hall advisor in college, one of my roles was sorting the mail, which has been useful experience years later: basically, you can ignore anything sent as “PRESORTED STANDARD”: https://www.thebalancecareers.com/how-to-spot-junk-mail-with...
The importance of a piece of mail is inversely proportional to its claimed importance.
I received my first paper nigerian scam last month!