I have all of our clients setup with email accounts on our mail server (redhat 2.4.20-28.9smp/sendmail 8.12.8).
I want email sent to user1 to stay as normal and email sent to user2 to be forwarded to an internal exchange server thats setup as a test.
I also need to make sure that mail comes into the same address, and goes out as the same address.
firstname.lastname@example.org -> sendmail.domain.com
email@example.com -> exchange.domain.com
but when they send email, the emails go out as firstname.lastname@example.org and email@example.com so I don't have to mess with MX records or forwarding ports on the firewall or anything.