[Exim] rewriting hosts

Hi guys

I have a list of internal hosts like

hostname.internaldomain.com

that needs to be rewritten to something like

hostname.publicdomain.com

when going out through exim, and the reverse when coming back in.

I suppose I can do this with a rewrite rule, but how can I easily use 1
file for

the rewrite rule lookups and the relay_to_domains lookup since after
rewriting the destination domain will become hostname.publicdomain.com

Thanks


Ronny