Set ML submission to moderated for non-subscribers
and few persons that check the backlog regularily.
Further add e.g. a 24 hours timeout (if possible),
so that nothing gets stuck unclassified forever.
This way the mails can get filtered out
and the regular traffic can reach the destinations.
I know several other ML systems, e.g. the gnome project,
where it works nice.
dont let your ML get misused as distribution system
the spammers messages.
-Alex.