I own a domain (actually a couple) - pretty easy to do these days, at about $10 each per year. I have configured the domains such that any received email not sent to a legitimate user gets forwarded to me as the domain owner. I get some mail that needs to be forwarded, usually due to name confusion. In the last month or so, there seems to be a new virus out in the world, because I am getting a huge number of "delivery failure" messages. The message I see is usually a "reply" to a supposed sender message informing me that the message cannot be delivered because of the contents (virus), but occasionally because the destination address is defunct or full. The supposed sender is some bogus user within my domain - not only a fictitious user, but often something completely bizarre (e.g., "fl8noj12" or "bz8ankladfy" - not even a phat name from some haxxor). My guess is that a virus is out there, sending mail using my domain to create a seemingly legitimate email address and hoping to capture someone who opens the mail.
The messages come from all sorts of interesting domains - .ru, .jp, .kr, and so on. Had I been clever, I would have put up a map with pins in it.
Spam - It Brings the World Together(TM).