[exim] How to test new configuration file

Hi,

I did some major redesign on my exim4-configuration file and would of
course like to test it before setting it productive.
I have a dedicated linux box for testing and stuff, so what I would like
to do is to copy all mails on the productive mail server and forward it
to the test box.
This itself is not the problem, a router like this seems to work

exim_testing:
driver = manualroute
transport = remote_smtp
route_list = * host.address.of.test.box
unseen

The problem here is the rejections of mail by the test exim. I have
smtp-time spam scanning activated, as well as virus scanning. So mails
would get rejected quite often. With the above setting, the productive
exim would send a bounce message to the sender, if the test exim rejects
the mail with a 5xx because of e.g. spam.

Is there a way to tell the productive exim to ignore the 5xx return code
when forwarding mails? Or, more in general, how to you guys test new
configurations on "real life" mails?

Thanks in advance,

Wolfgang