transition email server, same domain two servers

[Gene Delitzoy]

Hi,

I would like to move a mail server to a rh mail server, but I would like
to move x amount of clients per day to the new one, not a total replace
all at once. I was thinking of getting all mail sent to the new server
and then sending email to the old server until the user gets moved over.
Can I do this with .foreward files? same domain name, same username,
same email address. What could i do this with if the old email server is
windows one.
thanks