Mail - Sendmail

yum groupinstall "Mail Server"

Setup
Comment out
DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl
FEATURE(`accept_unresolvable_domains')dnl

Masquerade
MASQUERADE_AS(`mydomain.com')dnl

Access
Reject     - error message
Discard   - no error
Relay

Example
# by default we allow relaying from localhost...
Connect:localhost.localdomain           RELAY
Connect:localhost                       RELAY
Connect:127.0.0.1                       RELAY
Connect:127.0.0.1                       RELAY
From:example.net                        REJECT
Connect:example.net                     REJECT
From:user@domain.com              DISCARD

Domaintable
Allows you to map to different domains
the following will forward from example.com to example.org
example.com    example.org

Virtusertable
root@example.com                root
postmaster@example.com          postmaster@noc.example.net
@example.com                    joe