[exim] Unroutable Address for another local server.

Dear All,

I'm trying to add an additional server inside our local domain. We have
an Exim host which accepts our corporate mail; mail.ourdomain.com What
I'd like to do is add another machine which will become
mail2.ourdomain.com and to which internal domain users can address
messages to the accounts it on it.

Sounds simple enough. However despite all my efforts I either get
"Unroutable address" or even more bizarre to my simple mind, messages
addressed to user@??? end up in user@???
instead.

All I need is to be able to convince our Exim configuration on
mail.ourdomain.com to route messages on to mail2 that arre addressed to
user@???

Suggestions most welcome!

Thanks,

Steve