When I worked at Motorola, I had a little Garfield toy on my desk. I went away on a two-week business trip, and returned to discover that in my absence one of the other sysadmins had managed to break one of said toy's plastic eyes. So I set up a cron job to mail him every five minutes:
my poor cat, he's half blind
As soon as the guilty party realised that I'd automated this, he set up an elm filter rule to automatically discard the messages as soon as they arrived. Both cron job and filter remained in place for about a week, because we forgot about them. So for an entire week, one system was sending automated mail, and another system was automatically canning it.
I'm looking at my spamfilter folder at the moment, and wondering how many times this process is being repeated around the world right now.