Hi all, have a look at http://freshmeat.net/projects/qmail-monitor/
"qmail-monitor is a patch to qmail that offers mail monitoring (duplication) functionality on both incoming and outgoing SMTP traffic. the monitor ruleset is intuitive and allows the administrator to make changes without restarting the server processes"
you can define per domain, sender and recipient rules.
I installed it a few days ago and it seems to work good
Hope it helps
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