Hi

I'm trying to find out if this is possible.

I have an existing server (Server 2008 R2 AD Domain Controller) and I want to add an Exchange server (Server 2012 with Exchange 2013) to the same domain to utilise the active directory from existing server.

Is it possible to add the Server 2012 server box as a secondary DC (or similar) so that Exchange can run off the existing active directory form the Server 2008 box.

The reason I want to do this is to reduce the total cost of ownership by not having to buy more server user CAL's (instead use the ones we already own).

It's not recommended to install Exchange on a Domain Controller.

https://technet.microsoft.com/en-us/library/ms.exch.setupreadiness.warninginstallexchangerolesondomaincontroller%28v=exchg.150%29.aspx?f=255&MSPPError=-2147217396

Ok, can I have the Server 2012 box as an extra server in the existing domain (without it being a DC) and leverage the user CAL's from the existing Active Directory on the Server 2008 box?

You'll need an Exchange Server license, a Windows Server license, and Exchange user cals. I'm not a licensing expert, but I think the existence of the user CALs for the version of Exchange you have is all you need.

Ok but ultimately I am trying to find out if the Exchange Server will find the AD from the DC. I know that I have to have the exchange software + exchange user CAL's and also AD user CAL's equal to the number of mail boxes. From what I understand Exchange has to be installed in an AD environment.

Ok but ultimately I am trying to find out if the Exchange Server will find the AD from the DC. I know that I have to have the exchange software + exchange user CAL's and also AD user CAL's equal to the number of mail boxes. From what I understand Exchange has to be installed in an AD environment.

The Windows 2012 Server that you are looking to install Exchange on will need to be joined to the domain.  So the yes Exchange Server will be able to reach Active Directory.  

Ok great, do you know how the Windows 2012 Server should be joined to the domain without making it a secondary DC (i.e. joining it as a standard user)?

Hi,

We need add this Windows 2012 server to existed AD domain, and login as AD administrator.

Then begin installing Exchange server on that server, here's an article about Deploy a new installation of Exchange 2013: https://technet.microsoft.com/en-us/library/aa998619(v=exchg.150).aspx

Thanks

Ok great, do you know how the Windows 2012 Server should be joined to the domain without making it a secondary DC (i.e. joining it as a standard user)?

You can join the computer to domain by following this link:

http://www.howtogeek.com/99381/it-how-to-join-machines-to-your-active-directory-domain/