Hi,
I went through this and did two things:
1. On the Scalix server, I told Sendmail to send any unknown mail coming to domain.com to a specific server - which ran the old email system. I did this using the /etc/mail/mailertable file - I entered something like this:
domain.com ESMTP::[oldmail.domain.com]
Then do make -C /etc/mail. (my memory is a bit vague here since I did it a few months ago).
The other thing we needed to do on the Scalix server is to add in another email address in the console for those who were moving to Scalix. For example,
user@mail.domain.com. We then set up a forwarder on the old server, for those addresses which had moved over to the new server, to forward them to
user@mail.domain.com, which forwarded them to Scalix.
This worked for us.
Andrew.