[exim] Sender verify failed when sending email from internal…

Hi,

I have a working exim config that is used as our public smtp mail server.
But I also need to be able to mail alerts etc from scripts and programs on
our own servers.
So my problem is that from some of our servers when you try and send emails
(from command line or from programs such as nagios) to email addresses in
our domain I get an error:

50-Verification failed for <root@???>
550-Unrouteable address
550 Sender verify failed

and strangely (for me at least) I can send from other systems. The root
address mentioned above is a valid address so Im not sure what the problem
is. Emails sent from other domains are working without problems. Unless our
config is a particular mess hopefully its a common prob that someone can
easily identify...??? I hope ;)

anyway, if anyone has any tips that would be much appreciated,

thanks Andy.