[Exim] manual route to internal private ip

Good afternoon.

Can anyone help with a private ip problem.

My manual routing is working 100% for legal IP's

tom@??? gets rewriten to tom@??? and routed via
manual route.

BUT...

for private ip's, it fails

test@??? rewrites to test@??? but manual route
fails.

The ip of mxserver.domain2.tld is 172.17.x.x

Regards,

Tom Kinghorn