Converting to New Mail Server

We have about 350 users on our Visnetic Email Server. We are
converting to Novell Groupwise. Both servers have internal and
external IP Addresses. The Visnetic Server is setup with out ISP to
recieve email. Instead of just shutting down the old server and
turning on the new one we would like to move users over 1 at a time.
To do this we understand that we need to setup the forward option on
our Visnetic Software to foward any emails for that user to the new
groupwise server. The problem is it is not doing that. What do we need
to do to get this setup working. Anything in our DNS servers need to
be setup. Both server can ping each other by name and IP.

Thanks

Dan