I'm looking into what could be done to avoid duplicate message floods like the one today in the future, or at least lessen the impact. On the Qmail website I found a script for roughly this purpose at
http://www.qmail.org/eliminate-dups
from Russ Nelson. As luck has it I happen to know Russ so I spoke with him about this for a few minutes and he thought that it would be fine to use this on the listserver.
However I'm not going to jump into this too quickly because a faulty cure is likely to be worse than the disease. So I'm carefully evaluating this script and I would appreciate it if you could look over it and give your opinionl.
The idea is that this would just be stuck in above the existing line in ~list/.qmail-default and so work for all mailman lists.
Ken