Hi Falko, I'm pretty sure these didn't originate at my server. As far as I can tell from analyzing the logs, I think you are correct taht some spammer is usning one of my domains. I checked blacklist/greylist yesterday and the domain(s) I have are not blacklisted (yet).
My immediate problem is how can I use a mail script to dump these as they are filling up my admin mailbox? I tried setting email blacklist with the IPs as sender and client filters, and that helped. Do you have any other ideas to try?