At present I have two forests, let's say "old_forest" and "new_forest".
old_forest is a Server 2000 native forest with one domain.
In this domain is an Exchange 2003 organisation
new_forest is a Server 2008 native forest with one domain.
In this domain is an Exchange 2010 orgaisation.
I would like to be able to migrate users between the mail servers without affecting the user profile on the client desktops, so without joining the PC to the new_domain in new_forest. There are shared resources on old_domain in old_forest that I would need access to for users in the both the old_domain & new_domain (in new_forest).
Talking this around with my collegues, the ideal situation would be for users to remain on the old_domain (maintaining the desktop profile) but their mailbox/mail profile be on the server in the new_domain in the new_forest.
Eventually, the old_domain and the old_forest would be removed altogether as all new users will be added to the new domain.
I hope this makes sense! Please ask as many questions as you need!