I just spent two days fighting the NDR demons. Tried applying SPF protection for MIME: FROM values from my own domain ... Imagine ...
Finally got a Backscatter Spam patch from GFI on Monday, applied it Monday night and everything seems to be humming now.
Nothing like 11,000+ emails in the PreSubmissionQueue (and climbing steadily) to cause some stress.
Damn Spammers. Punch one for me. Until unconscious.
All The Best,