The problem is how do you tell the difference between someone posting a
direct reply and some posting something new?
Bell is *not* bouncing the mail but rather replying to a message with a new
message. The same is the case with e.g., the vacation program.
One potential mitigator would be to have the list throttle the number of
posts that any single poster can make during a given period of time. I can
think of lots of problems with that sort of solution but it's a
possibility. Unfortunately, I don't see any all-purpose, general
solution.
Take care,
John