I tell my email (Outlook, by corporate fiat) to let me know when someone has read an email I sent them. This leads to some interesting messages like this one:

Your message
To: (list)
Cc: (another list)
Subject: (program) Usage
Sent: 10/30/2004 9:38 AM
was deleted without being read on 11/18/2006 8:20 AM

Well, I’m glad he got his inbox cleaned out.