I'd like to get some feedback on my plan of action from some of the experts out there.
The Situation: I've picked up a new client with 4 domains across 3 forests with two different Exchange 2003 organizations. The environment is unhealthy. There are replication issues and other various problems caused by a malware outbreak. To resolve this and simplify the network configuration, I am creating an entirely new forest, domain, and Exchange 2010 organization. The existing Exchange setup consists of 9 accepted domains between the two servers. Each one has its own set of domains.
The Plan: The client wants to retain all 9 of the mail domains and obviously wants no disruption in mail flow between the organizations. I've already built out a new domain and setup the Exchange 2010 servers. I have added all of the mail domains as accepted domains. I have set them all as Internal Relays and have placed a temporary connector to forward to the appropriate smart hosts. As I understand from my research, this should allow any unresolved mail on the new Exchange org to get relayed to the old Exchange 03 orgs. Is this correct?
From a mail flow standpoint, all 3 of these Exchange organizations are currently internet facing. I am switching them to a 3rd party spam filtering service for the new org. I realize that manipulation of public DNS will ultimately determine where the mail is going. If I stand up the new organization to receive all mail first then relay out accordingly, how can I still continue to make Active Sync work on the legacy environment? Due to the state of the network, it has been decided that users are going to be created on the new domain and then mailboxes will be imported via PST one at a time. As far as Active Sync is concerned, if I left all 3 mail servers internet facing and had MX records point to the new server and then setup public records for mail, mail2, and mail3 I should then be able to point Active Sync devices to the appropriate host. Is this correct?
I apologize for being so long winded on this. I would appreciate any feedback or suggestions anyone has.