Spammers are thwarting filters by putting their target email addresses in the sender line, and pushing the emails to invalid addresses, according to The Register.
I’ve received about a half dozen bounced messages that may be related, and recollect they were coming from Postfix servers. If you see one, you will notice all the generic “this is a message from the Postfix server” bit, and the “returned” spam message will be at the very bottom.
I’ll post a sample here next time one comes my way.
PS: Yes, that title needs work.