Someone is doing something rather common, spoofing my domain name; it's equivilant to sending out letters via the post office, and using someone else's address for the return address so they don't just ignore the message, recognizing who it's from.
Anything I actually send will show from firstname.lastname@example.org, or, in rare circumstances, email@example.com. Anything else? It's spoofed e-mail.
If you want to actually try to deal with it... check the headers.. See what the IP address it came from was, and e-mail it to the postmaster THERE. They may be able to help. I can't.. They are just using my name.
-keith h weston