Recently, I've had a lot of email questions come in on certain topics related to Exchange Server 2007.  I thought I would gather up the most frequently asked ones and post them along with the answers here.

Q1.  Does the Edition of Windows Server need to match the edition of Exchange Server (Standard vs. Enterprise)?
A1.  No.  You can use Windows Server 2003 Standard Edition with Exchange Server 2007 Enterprise Edition or Windows Server 2003 Enterprise Edition with Exchange Server 2007 Standard Edition.  The key here is to match up any capabilities that are required based on features / functions you plan to use.  For example, if you are using Exchange Server 2007 Enterprise Edition because you want to take advantage of CCR, then you MUST be running this on Windows Server 2003 Enterprise Edition (or Server 2008).  Cluster support is not available with Windows Server 2003 Standard Edition.  On the other hand, if you are using Exchange Enterprise Edition to go beyond the 5 SG limit, then you can run it on Windows Standard Edition provided the memory limits are fine (along with any other differences between Windows Standard and Enterprise).  Just remember, for production purposes, you MUST be running x64.

Q2.  Do I really need a 64 bit machine to run the Edge Transport Server??
A2.  YES!!!!!!  All Exchange Server 2007 Roles MUST be installed on an x64 copy of Windows Server 2003 or 2008 if it is to be used in production.

Q3.  If I implement a CCR cluster, what is the minimum number of Exchange Servers I need?
A3.  The CCR cluster will take 2 servers (1 Active; 1 Passive).  Then you will need a third server to install the Hub Transport (HT) and Client Access Server (CAS) Roles.  These two roles can co-exist on this third server.  Therefore, the bare minimum number of servers when using a CCR is Three.  However, if you are using CCR to provide redundancy for your Mailbox role, you may want to provide redundancy for your HT and CAS roles as well.  If you choose to do that, then you would need a minimum of Four servers so you can have two servers that are running HT and CAS.  Now, if you want to add an Edge Transport Server role into the mix, that will require at least one more server (two or more if you want redundancy of the Edge Transport too).

Q4.  Licensing of Exchange Server 2007 (I know, but I keep getting these).  Please help clarify Server versus Client Access Licenses (CALs) as well as Standard versus Enterprise.
A4.  You can mix and match Server editions (Standard and Enterprise) with CAL editions.  For example, you can have 2 Enterprise Server Licenses while using 200 Standard CALs.  The Server edition you will need will depend on the server side features you are trying to use.  For example, CCR requires Enterprise; 20 Storage Groups requires Enterprise.  If you don't use the features that require Enterprise, you can use Standard.  So if you look at Q3, you may have 2 Enterprise Editions for the Mailbox CCR, but 2 Standard Editions for the HT / CAS roles.  For the CALs, you will ALWAYS need to have Standard Edition CALs for users that logon to Exchange.  In addition to the Standard CALs, you may need some Enterprise CALs depending on Client Features in use.  For example, if you have 200 users who will have their mailboxes hosted on the Exchange 2007 servers, you will need 200 Standard CALs.  If 100 of those 200 users need to have Custom Managed Folders, you will need to add 100 Enterprise CALs in addition to the 200 Standard CALs you already have.  More info on licensing can be found here: http://www.microsoft.com/exchange/evaluation/editions.mspx.

Q5.  If I have multiple AD sites with Mailbox servers in them along with 1 CAS and 1 HT, what happens if the CAS and / or HT goes down?  Will the CAS / HT in the other AD Site(s) provide redundancy?
A5.  For every AD Site that has a Mailbox server role, you must have at least 1 CAS and 1 HT role in that AD Site as well.  The CAS and HT roles will only communicate with the Mailbox role in the same AD Site that it resides in.  So the CAS and HT in Site A will not be able to communicate directly with the Mailbox server in Site B and Site C.  If your CAS or HT server in Site A goes offline for any reason, the CAS or HT servers in Site B and Site C will not provide redundancy for the one in Site A.  To provide redundancy of the CAS and HT in a given AD Site, you will need to deploy more than one of those roles.

This is not the entire list of questions I've received regarding Exchange Server 2007, but these 5 seem to be the ones I get again and again.  I hope this helps.

Harold Wong