[CentOS] sendmail routing

CentOS 4.8, sendmail 8.13

Hi All:

I have a couple of questions regarding the routing of outgoing emails.
I have spent several hours doing Google searches but I have not come
close to what I am looking for. If someone can give me push in the
right direction I would greatly appreciate it.

We currently have three domain names (two for our development company
and one for our production company). We have one mail server in our
development office that hosts all three domain names. Actually we
just treat the three domain names as aliases of the mail server (via
the local-host-names file and I do not see a need to change this. What
I would like to do is route (relay?) any outgoing emails that are
from emails addresses using only one of those domains to a separate
SMPT server.

1. Is this possible?

2. What is it called?

3. Can you provide examples or links to relevant docs?

TIA

Regards, Hugh

-- 
Hugh E Cruickshank, Forward Software, www.forward-software.com