Is it any of your business, as list owner, what people send
off-list? Even if it's in response to list traffic? Who appointed you
the censor of all that someone else sends?
If someone misconfigures a vacation autoresponder to spam your
list, then by all means, ban the loser. But what gives you the idea that
you have any right to ban someone from a list for something that was not
sent to the list? How would you feel if someone banned YOU because they
dislike your spam filter?
Oh, I'm not saying you can't, but if you act arbitrarily and
unfairly, you'll kill your list...who wants to be on a list with an
unpredictable, arrogant list-owner?
From what the original poster has said, the guy running the
autoresponder hasn't done anything wrong. If anything, he's being polite,
and letting people who send him mail know that he's on vacation and can't
answer right away. Given the number of rude jerks on the internet, do you
really want to punish someone for being polite and thoughtful?