[exim] How to detect child messages?

Hi,

I use a manualroute router with the unseen option to copy mail to an
another host. If the original recipient is rewritten (let's say
mail@??? is rewritten to peter@???), then
there are two new mails produced and send to the other destination. If
peter@??? was an alias, too, there would even be more
mails.

So the question is: In a router, how can I detect if the current message
is the one received via SMTP, or a subsequent message where the
recipients are already rewritten?

I tried using the "redirect_router" option and setting it to the next
router, but it doesn't work. The manual says, "redirect_router" option
"causes the routing of any generated addresses to start at the named
router instead of at the first router". I don't know why it doesn't
work.

Thanks,
Peter