Exchange Server 2007 and Exchange Server 2010 are similar in architecture so the transition process is more straightforward. The following procedure illustrates a typical transition from Exchange Server 2007 to Exchange 2010:
Each site in Active Directory should have at least one PDC, schema master and the Global Catalog server on a Windows Server 2008 SP2 level. It is recommended to have 64-bit type Domain Controllers and Global Catalog Servers for optimal performance preferably Windows Server 2008 x64 SP2 or Windows Server 2008 R2
Backup Active Directory global Catalog servers, Exchange servers and Servers that interoperate with Exchange Server, such as gateway systems or replicated directory servers. It is also a best practice to turn off any replication to other environments during the transition process, such as Forefront Identity Manager (previously named ILM, MIIS, IIFP, and MMS).
Migration from Windows 2003 AD Forest to Windows 2008 AD Forest and Forest Preparation
Once you have finished prerequisite, you have to take the installation order of the Exchange Server 2010 servers into account to minimize the impact:
Exchange Server 2010 Mailbox Server. After you have installed the Mailbox Server role and established a proper Public Folder replication between Exchange Server 2007 and Exchange Server 2010, you can start moving mailboxes to the new Exchange 2010 Mailbox Server. Of course, the Public Folder replication needs only be configured when Public Folders are used in Exchange Server 2007.
The Edge Transport Server can be installed at any time, since an Exchange Server 2010 Edge Transport Server can be subscribed to an Exchange Server 2007 SP2 Hub Transport Server. Use Export and Import option for all policies applied in previous ET server.
Transitioning from Exchange Server 2007 to Exchange Server 2010
1. Prepare Windows Server 2008 (RTM or R2) x64 edition server for the first Exchange 2010
2. Install the AD LDIFDE tools on the new Exchange 2010 server (to upgrade the schema).
3. Install necessary prerequisites (WWW for CAS server role) including web certificates.
4. Install CAS server role servers and configure per 2010 design. Validate functionality.
5. Transfer OWA, ActiveSync, and Outlook Anywhere traffic to new CAS servers.
6. Install Hub Transport role and configure per 2010 design.
7. Transfer inbound and outbound mail connector to the new 2010 HT servers.
8. Install mailbox servers and configure Databases (DAG if needed).
9. Create public folder replicas on Exchange 2010 servers using Exchange 2010 Public Folder tool.
10. Move mailboxes to Exchange 2010 using Move Mailbox Wizard.
11. Re-home the Offline Address Book (OAB) generation server to Exchange Server 2010.
12. Transfer all Public Folder Replicas to Exchange Server 2010 Public folder stores.
13. Delete Public and Private Information Stores from Exchange 2007 servers.
14. Remove Exchange 2007 Edge Transport subscription
15. Uninstall all Exchange 2007 servers.
The following key factors differentiate a 2007 to 2010 transition from a 2003 to 2010 transition:
One added advantage of transition from Exchange Server 2007 to Exchange Server 2010: if Outlook clients are at 2007 levels or above, the move mailbox process does not result in downtime, making the end user transition experience completely transparent.