Exchange Server 2007 – 2010 coexistence - figuring out external DNS

I have introduced a 2010 exchange server to my exchange 2007 environment and am working to get them to coexist.

I have ONLY 1 exchange 2007 server with all roles installed on it for email to function properly. I have introduced a new exchange 2010 server and it will be setup the same exact way with all roles installed on ONLY itself for email to function properly.

I have successfully moved the OAB, Public Folders and 1 test mailbox to the new exchange 2010 server and now need to setup OWA and autodiscover to be reachable externally.

right now it works internally properly!

Meaning that if i open a browser inside the network and goto to the internal FQDN ( for the new 2010 exchange server and try to log in as a mailbox user on the exchange 2010 server it will open their mailbox and if I login as a user whos mailbox is NOT on the exchange 2010 server (and the mailbox resides on the exchange 2007 server) it will redirect me to the exchange 2007 OWA site and i can log in with no problems and see mail.

Now according to this article I need to somehow swap the DNS names and change the name of my existing exchange server:

can someone be a little more clear about what i need to do in my particular case?

Here is my current setup info:

exchange 2007 FQDN server name:
external 2007 OWA address:

new exchange 2010 FQDN server name:

What i would like my external address to be for this:

Please note that i am currently redirected to exchange 2007 OWA site when I enter the address above externally ( but i am unable to login to the test mailbox that i have moved to the exchange 2010 server - it basically shows this page when i try to log in:


I am however able to log in externally to that address above ( for a mailbox that resides on the exchange 2007 server with no problems. I find this strange as I have always given out For OWA access info....

So does this mean there is an existing redundant A record in my external DNS that is going to my exchange 2007 server?
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Belal KhalladConnect With a Mentor SR ConsultantCommented:
so you need to have a static IP address for the (Exchange 2007 URLs) and a static IP address for (Exchange 2010 URLs) . so externally when you type and your mailbox exist on Exchange 2007 , it will perform a redirection to  which is your exchange 2007 mailbox and automatically logs you in. for this to occur you need to ensure you have all Urls correctly configured.

so you will need 2 static IP address one for ( exchange 2007 URls) and one for ( exchange 2010 URls) .

so all existing urls that are currently pointing to Exchange 2007 needs to point to Exchange 2010.

this should work flawless provide you have all external and internal Urls and DNS configured correctly .
Belal KhalladSR ConsultantCommented:
•Change DNS to repoint to the IP of 2010 CAS
•Create new DNS record and point to IP of 2007 CAS
•Change ExternalURL on 2007 owavirtualdirectory to
•set ExternalURL on 2010 owavirtualdirectory to

Based on your post, sounds like I do not need to change 2007 Outlook Anywhere ExternalHostname or AutoDiscover URI's (from to Is that correct? Same for ActiveSync, or does that one need to be changed also (mail -> legacy)?

IT_Field_TechnicianAuthor Commented:
Thanks for your help Balal!

So if i need to:

Change DNS to repoint to the IP of 2010 CAS

then that leads to other questions about my firewall port forwarding rule that i currently have setup for my existing exchange 2007 server.

How do i handle this?

Can i use the same external WAN IP address for my port forwarding rule and just update the port forwarding rule to point to the internal static ip of exchange 2010 server?

Or do i need to have another availble static IP address and create a brand new port forwarding rule to point port 25 traffic to the new exchange 2010 server?
Ajit SinghConnect With a Mentor Commented:
IT_Field_TechnicianAuthor Commented:
It worked - Thanks!
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