3. If I drop my Exchange 2007 servers, will I lose WebDAV support for Mac Entourage clients?
Entourage, which is Microsoft's Mac OS X client for Exchange, can connect to the Exchange environment using the WebDAV protocol or the POP and IMAP protocols. WebDAV provides more capabilities than POP and IMAP, which provide just basic send/receive functions; commonly, WebDAV gives Mac users access to most of Exchange's capabilities. But Microsoft is dropping WebDAV in Exchange 2010, replacing it with Exchange Web Services (EWS), which it says will support more Exchange capabilities than WebDAV (Entourage's inferior capabilities compared to Outlook is a frequent complaint of Mac users). So you'll have to move your Mac users to the EWS-capable version of Entourage, which Microsoft recently made available for download, or switch to the forthcoming Outlook for Mac client that Microsoft says will replace Entourage next year. You have two other options to maintain access to Exchange functionality if you're not ready to go the EWS or Mac Outlook routes: One, if your Macs run the new Snow Leopard OS, you can use the included Apple Mail client instead. Two, you can keep an Exchange 2007 server in the mix for WebDAV connectivity since Exchange 2007 and Exchange 2010 can coexist peacefully.
4. Can I have Exchange 2008 coexist with Exchange 2000 or 2003, then complete the transition to Exchange 2010 later?
Exchange 2000? No. Exchange 2003? Yes. For Exchange 2003 and 2010 to coexist, you have to change your organization to native mode on an Exchange 2003 server. What does that mean? Well, mixed-mode Exchange typically means you have Exchange 5.5 or Exchange 2000 servers intermingling with your Exchange 2003 organization, but it is time to drop those legacy servers and become all-Exchange 2003 shop. You'll also have to switch to native mode in your Exchange 2003 servers. Only then you can begin implementing your Exchange 2010 servers for coexistence and transition.
5. What should I have in place within my Exchange 2003/2007 environment before I implement Exchange 2010?
At the bare minimum, your Exchange 2003 and 2007 servers should be running Service Pack 2. At least one Global Catalog server in each site should be running Windows Server 2003 SP2. ActiveDirectory must be in the Windows Server 2003 forest functionality mode while transitioning.