It seems spammers are spoofing email addresses from my domain again. I've been getting all sorts of bounce messages and out-of-office replies. In the past this has died down pretty quick, but this time it seems to have been going on for about two weeks, so whoever is doing it is a persistent bastard.
I'm currently investigating adding an SPF entry to my DNS record. That should cut down on the spoofing to some degree. The lack of an SPF entry may be why the jerk picked my domain anyway. Stay tuned...