Dave Warren:
It would be fantastic if the list operators were to track this down and kill it off. My guess is that there is an address subscribed which receives the list and triggers the spam to be sent (at least based on seeing this type of thing on a few other lists over the years).
Quirky idea, and totally one I've quietly thought about for a while with various lists...
Especially if we could correlate spam with posts.. but then that can be a lot of work partially because of spam filters.
Spam/UCE is a hard never-ending war.. what you could do with reverse DNS lookups twenty years ago was such a dream.
The smartest option for mailing list participants is to use a separate address for mailing list(s).. if you aren't in a position to control your MTA.
g