Ever wondered what happens with ActiveSync relationships on mobile devices when you replace the Exchange server published to the internet?
1. If you move a mailbox from Exchange 2003 to Exchange 2003 or to Exchange 2007 RTM, you have to recreate the partnership manually.
2. If you move mailbox to Exchange 2007 SP1, there is no need to re-create the partnership manually.
3. Please note the certificate should be the same. Otherwise, you will encounter issues with certificate in Exchange ActiveSync.
For more information on how to re-create the partnership manually, see this article on the Exchange Team
In previous versions of Microsoft Exchange Server, if you moved your mailbox to an upgraded server (such as Exchange Server 2003 to Exchange Server 2007 RTM) re-creating the partnership was required. However, if you move your mailbox to an Exchange Server 2007 with Service Pack 1, the new Sync State Upgrade feature is built into Move Mailbox and will allow you to continue synchronizing your device without resetting your partnership.
For more information on the Move-Mailbox cmdlet, see this article on TechNet.
In Exchange 2007 Service Pack 1 (SP1), if you move a mailbox to which a mobile device is synchronized using Exchange ActiveSync, the sync state of the mailbox is updated automatically during the move. You do not need to perform any additional steps, and the user does not need to again sync the device after a mailbox move.
Although you don't move mailboxes, if you add a CAS server and users use the CAS server to maintain their Exchange ActiveSync access, you need to note the following:
In order for your users to continue to synchronize their mobile devices via Exchange ActiveSync with their mailboxes hosted on Exchange 2003 mailbox servers, you will need to ensure that Integrated Windows Authentication is enabled on all of the Exchange ActiveSync virtual directories (Microsoft-Server-ActiveSync) on Exchange 2003 mailbox servers.
For more information on how Exchange 2003 mailboxes are maintained after the Exchange 2007 CAS role are introduced in the environment, please see this article on the Exchange Teams blog.