forwarding questions

[3RiversTechAdmin]

Hey,

I have a couple of questions regarding fowarding.

1. My zimbra box is not production right now and I want to migrate the test users over. Now zimbra can send messages out of course, but becuase messages inbound currently end up with the old sendmail e-mail server what I tried to do was use .forward files to forward the testing user's e-mail to zimbra. At first I thought it was not working, but after looking at the logs I have found that zimbra receives the e-mail, then sends it back to the old server . The message proceedes to bounce back and forth untill the limit set on the sendmail server is reached. I don't know why this happens. I can send mesages to the zimbra machine over IMAP or SMTP fine.
Perhaps I setup my .forward wrong,
if YYY is the old mail server and
XXX is the new mail server,
and the e-mail address for the user is user@3riverstech.com
on YYY /home/user/.forward contains:

\user
user@XXX.3riverstech.com

2. Also, I was wondering how I can setup zimbra to forward a whole domain to a mail server(two businesses share the network external interface)

Thanks in advance