Hello All- I have an environment I am working on and would like to get some input. There are 3 non-internet facing AD sites that hold 2007 Mailbox and CAS servers, Site1, Site2, Site3. All users access OWA and Active Sync through one internet facing site, SiteA. Currently no ExternalURLs are configured on any virtual directories and the environment exists using CAS proxying. We are planning to introduce the first Ex2010 CAS in SiteA (internet facing), and I am struggling with how the redirection/Proxying is going to work. My plan is to set up the legacy.contoso.com namespace, route that traffic to the 2007 CAS in SiteA and associate the mail.contosoc.om traffic with 2010. I was then planning on configuring ExternalURLs for the OWA and Active-Sync virtual directories in the 2007 virtual directories for legacy.contoso.com - but based on my reading I am afraid that this will create a CAS loop (The ExternalURL parameter will always be used on the non-internet facing CAS servers, and proxying to them will never occur). Can someone advise to the optimal configuration for 2007/2010 Coexistence in this scenario?? thanks! roc

Further reading indicates the correct config is to populate the ExternalURL values for OWA and Active-Sync for SiteA CAS servers. http://blogs.technet.com/b/exchange/archive/2009/12/08/3408985.aspx http://blogs.technet.com/b/exchange/archive/2009/12/02/upgrading-outlook-web-app-to-exchange-2010.aspx It seems that 2010 can proxy OWA/AS to 2007 in non-internet facing sites, in a situation like this where 2007 is already proxying to regional sites (no redirection) - it seems like I shouldn't have to setup a legacy namespace at all - and could just migrate the current namespace to 2010 and have it proxy to 2007 (by not configuring external URLs for them at all). Is this a valid approach??

Hi, I think we may need to configure the following settings. 1. A record: legacy.domian.com exchange 2007CAS domian.com Exchange 2010CAS 2.ExternalURL: it should be configured on OWA virtualdirectory on Exchange 2010 CAS server. You can run cmdlet Set-OwaVirtualDirectory -externalurl legacy.domain.com. 3. Make sure the urls which list below can be accessed from internet. https://domian.com/owa https://legacy.domain.com/owa More related information to share with you: OWA Cross-Site Silent Redirection in Exchange 2010 SP2 http://blogs.technet.com/b/exchange/archive/2011/12/12/owa-cross-site-silent-redirection-in-exchange-2010-sp2.aspx Xiu Zhang TechNet Community Support

Thanks for the reply. I understand the process, I guess I just don't understand why Ex2010 can proxy to 2007 servers in remote AD sites, but not to 2007 servers in the same AD site.

Hi, Yes. That is by design. An Exchange 2010 Client Access server will never proxy Outlook Web App requests to an Exchange 2007 Client Access server in the same Active Directory site. All requests within the same Active Directory site are redirected to an Exchange 2007 Client Access server, using either the InternalURL or ExternalURL properties for Client Access server, depending on which properties are configured. Xiu Zhang TechNet Community Support