testing MS with copies from postfix

[Eric Dantan Rzewnicki]

I have configured a test box with MS and postfix. How can I get our
existing mailserver to copy all received messages to the test box?

The existing mailserver runs postfix as MTA with amavisd doing virus
scanning. Is there a way to tell postfix to send a copy of each message
received for foo at domain.org to foo at testserver.domain.org before amavis
gets it and before aliases are expanded without affecting normal
delivery on the existing server?

When testing amavis a year ago I set up a simple procmail recipe on our
existing non-virus-scanning server that did a simple copy of every
message delivered to any user at domain.org to a single
testaccount at testserver.domain.org. This time I don't want to do that,
because I want the MS box to get a copy of each original mail,
virus(es) and all, without having aliases expanded.

I've looked at the transport map, but that seems to be only for
redirecting mail, not copying it.

Thanks in advance for any suggestion,
Eric Rzewnicki