When I worked on a notification system that sent over a billion messages a month. We received spam complaints on emails sent 6+ years ago. No correlation, just a one-off spam complaint. I always wondered why this was happening.
Probably because people like me finally had some time to go through an inbox with 20,000 unread messages. Almost anything that's been unread was either (most likely spam) or (very rarely) just simply unimportant.
