Here's a basic procedure I was planning to use to migrate from Redhat 4 es sendmail with dovecot to Zimbra Open source....

a Backup to tape...(duh).
1 Backup to disk for useability.
2 Cat /var/spool/mail/$username > /home/$username/mail/old_inbox.
3 Make a tar file of all users /mail folder in their home dirs.
4 Stage new server.
5 Create users.
6 find out where the h&(&* the home dirs are and see if my /home/$username/mail/ files are in the proper format...
7. move and chane permissions of files (mail folders)...
8 Test
9 Deploy
Are there better tools for this?
Anyone do a sililar migration?