What operating system are you using?
SunOS 5.11
What system provides your mail account(s)?
As far as I can tell it's mailx
Is the spam that has been redirected into your three spam mail files all from a single mail account? Or, are the three spam files for three different mail accounts?
By far, most of it goes in mail/spam. Occasionally it goes in the others. Can't really tell what the difference is between these pieces of spam that would send them to different places.
Is there anything in the mail headers in the mail in those spam mail files that identifies what system, spam detector, or "agent" directed mail to those folders? Could some of the spam be detected by your ISP's mail processing system and some spam be detected by your local mail reading software?
That's actually a very good point. I need to look more carefully, and see in the mail files themselves who sent it there.
Do timestamps on the messages in those three mail files indicate that all spam was delivered to a single file for a period of time, siwitched to another spam mail file for another period of time, and then switched to the 3rd spam mail file? Or, is mail being directed to all three files during the same time period?
As far as I can tell, it's the latter.
Did you change any mail or spam assassin settings around the time when spam mail started appearing in your three separate spam mail files?
Nope.
I was just wondering if these spam folders were recognizable by their names.
Perhaps not.
Now, I think these spam files appeared when there was an OS upgrade, from an earlier version of SunOS.