And, heh! I note that cleanarch is now _part_ of Mailman, and apparently has been for quite a few versions. At the time Marc Merlin gave me a copy, it was beta.
Anyway, a real life-saver. Otherwise, if you don't use it to 'lint' mbox files, you'll find that /var/lib/mailman/bin/arch trips over unescaped "From " sequences beginning lines of message text. You end up with fragmentary garbage messages in the HTML pipermail archive, and have to go back into the mbox, find the problematic line of message body text, escape that line, try again, iterate until it drives you crazy or you find them all.