Exchange 2010 Coexistence

Exchange 2010 Coexistence Question:

I am in the initial planning phase of installing a new Exchange 2010 server in our organization. I have done quite a bit of research but there are still a few things that are not clear to me. We are currently running an Exchange 2003 server. My plan is to install 2010 in coexistence with that server. Here are some of the questions that I have:

1. Is there any reason that I should not prepare the AD schema now? I may not install Exchange 2010 for a month, but I was wondering if will hurt anything if I run the schema updates ahead of time.

2. The first role that needs to be installed is the Client Access role. We use ActiveSync for our mobile phones. Is there anything that needs to be addressed prior to installing the CA role in regards to ActiveSync? I know firewall rules, etc. will need to changed eventually to accommodate the new server, but is it necessary to do it prior to installing the CA role on the new server?

3. Are there any other pitfalls that some of you may have come across with a similar installation scenario?

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Glen KnightCommented:
1. Absolutely makes no difference if you do it now or at installation.


In a mixed environmnent the Exchange 2010 CAS server will redirect requests for legacy systems to the legacy URL.
For this to work, in your external DNS you need to have the following (they are examples so may not be exactly the same as the way you have it setup. should point to a public IP address dedicated for your legacy exchange environment.  This needs to be routed to port 443 on your legacy system using the source IP address associated with this A record. should point to a public IP address dedicated for your new Exchange 2010 CAS server.  This would normally be your existing A record reconfigured to use your Exchange 2010 CAS server instead of the 2003 server.

This is true for OWA.

However, for ActiveSync it doesn't redirect, it does actually proxy therefore the is not used when ActiveSync is being requested.  The mobile device will connect directly to the CAS server.

The other thing that is confusing me is you talk about an MX record.  The MX record is what other servers use to connect to your exchange server to send it email.  This in turn should be configured to use an A record.  In a lot of cases, this will be the same as the OWA A record.  In the example I have used here it should be

So your external DNS should look like this, assuming you have 2 pubilc IP addresses of and

MX Records should have the data of
A record for should be
A record for

Your router should be configured to forward port to the Exchange 2010 internal IP address and to the internal IP address of the Exchange 2003 server.
The only ports that need to be forwarded are port 443.

You will also need to have a SAN/UCC certificate with the following names in it, installed on BOTH Exchange servers. (the external URL for the 2010 server) (the external URL for the 2003 server) (where is the part after the @ in your email address)
cas2010.domainname.local (the internal fully qualified domain name of the Exchange 2010 server)
legacyexchange.domainname.local (the internal fully qualified domain name of the Exchange 2003 server)

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