My company just bought another company. What I'm curious about is the following? We are planning on migrating to a Windows 2008 AD backbone from Windows 2003 Enterprise 32 Bit R2 with one Active Directory domain. We will be hosting our own Exchange 2010 and upgrading from Exchange 2003. We would like to have one AD forest and have the exchange 2010 host two domain names. Can I have one set of users on the a.com (example) using the a.com domain email system and another set of users using the a.com AD connected to mailboxes of the second email domain b.com? Or would it be better to just keep two forest AD systems with their own individual exchange systems and just uprade all backends to Windows 2008 with an Exchange 2010. Then just create a trust between both networks?

Hi, An Exchange forest can host as many authoritative domains as you want - so the answer to your question is yes. I would recommend that you only create one forest - in this way it is much easier to have only one global address list ( I assume that this is what you want) Leif