The first issue we had to deal with was the domain controllers - although Exchange 2007 and Windows 2000 domain controllers can co-exist, at least one domain controller must be running Windows 2003, the global catalog must also be running Windows 2003 so the decision was made to replace all the domain controllers with Windows 2003 based systems.
Using Microsoft best practices, the domain controllers, network related services and FSMO roles were replaced with no downtime for network users.
All client machines and citrix servers were upgraded to Outlook 2003 by the IT support team to ensure connectivity to the new servers.A 2 server Exchange system was chosen, with the mailbox and hub transport roles on one of the servers, and the client access role on the second.
The mailboxes were moved over a weekend, with downtime to the users limited to when own mailbox was actually moved from the old to the new server. The mailboxes were distributed across four mailboxes stores for load balancing and user policy management purposes. Enterprise Vault and Blackberry enterprise were setup to connect to the new Exchange system and tested by internal and external users.
Once the mailboxes were moved and the Exchange system services were relocated to the respective server, the old Exchange servers could then be de-commissioned.
Before this was done incoming SMTP mail from the edge firewall was routed to the new mailbox server, and webmail requests were routed to the client access server. The user morale has increased dramatically as they are no longer waiting for their computer to catch up with what they are doing.
The support team are now not over worked as the support queues are smaller they even have time for personal development. The management are confident that in the event of a hardware failure, they could have the servers running again within hours and were confident the new infrastructure would perform very well for at least 4 years.
Once the project was completed, the in house support staff were trained on basic Exchange server operations - and were shown how to perform mailbox and mailbox store restorations.
The entire system was then documented and signed off by the IT staff at BFI.