Exim questions, inc. use Exchange Server?

[Rory Campbell-Lange <rory@campbell-lange.net>]

I'm trying to send mail from my linux box to the outside world. Our
office's mail server is MS Exchange on NT4 on address 10.0.0.6. My linux
user name is 'rory' whereas my office mail address is 'rory.cl'.

Previously I had Exim sending mail out to the web, but the headers
showed that the mail came from 'rory@x.com' instead of 'rory.cl@x.com'.
Is it possible to rewrite the headers?

I now have Exim pointed to send through the Exchange Server. However I
get the following error message:

rory.cl@x.com: lookup of host "10.10.10.6" failed in smarthost router.

Am I trying to send mail to Exchange over SMTP, and Exchange rejecting
it? My Macintosh client sends mail through 10.10.10.6 fine, including
mail with the "from" address not in our local domain!

Clearly I'm in need of an Exim setup tutorial. I'd be grateful for
pointers.

Cheers!
Rory