[exim] Add Unroutable local address

Hi,

New to Exim, using CentOS5.4. I have exim server which is receiving emails
from Internet, fine for the local user dani. However i have another
local cluster with 192.168.x.x ip addresses. Email generated from that
cluster comes as root@??? and which exim is rejecting as:

  dani@???   (ultimately generated from support@???)
    SMTP error from remote mail server after RCPT TO: dani@???:
    host mail.mydomain.com [x.x.x.x]: 550-Verification failed for
root@???
    550-Unrouteable address
    550 Sender verify failed

How i can add this local domain as valid sender to receive email.

Thanks
-dani