Q. If I migrate from a single Microsoft Exchange Server 2003 server to a single Microsoft Exchange Server 2007 server, will my Microsoft Office Outlook 2003 clients still be able to use their free/busy information?
A. Exchange 2007 implements an availability service to host free/busy instead of a public folder in Exchange 2003; however, clients prior to Outlook 2007 can’t use this service. They require the public folders. Assuming you’re making a standard migration in which the Exchange 2007 server joined the Exchange 2003 organization at installation for mailbox migration, you can still use public folders. Exchange 2007 needs to be configured as a public folder replica to allow free/busy information to transfer to the new server.
Prior to removing the last Exchange 2003 server, you need to be sure that the Exchange 2007 server hosts a replica of the public folder hierarchy with the Schedule+ Free/Busy system folder. Legacy free/busy should be available when installing an Exchange 2007 server into an Exchange 2003 organization as Exchange 2007 will include a public folder store for it. Outlook 2003 clients will not have connectivity issues if this is followed. You can find more information about this topic in the deployment guide for Exchange 2007. Also see the Microsoft TechNet article “How to Install Exchange 2007 in an Existing Exchange Server 2003 Organization.” As always with a new deployment, testing should be carried out to ensure correct operation.