Currently setting up co-existence between Exchange 2007 and 2010. Both are in the same internet facing AD site. Using the Exchange 2010 deployment assistant I have installed the CAS and HT. I have obtained the new certificate with the required legacy domain names and installed it on both my 2007 CAS and 2010 CAS. I am about to change the DNS records so that legacy.xxx.com points to my 2007 CAS and mail.xxx.com points to my new 2010 CAS. Problem is I am finding conflicting instructions. In the following doc it indicates I need to modify the OWAvirtualdirectory setting among others on the 2007 CAS server to the legacy values. Oddly the deployment assistant makes no mention of needing to do this. I have figured out that I do need to change the -OWAvirtualdirectory setting on the 2007 CAS for Autodiscover to function properly but why doesn't the deployment assistant mention this step? http://blogs.technet.com/b/exchange/archive/2009/11/20/3408856.aspx 11. You will then schedule Internet protocol client downtime (please note that this downtime window should be relatively small - enough time for you to make the change and validate that everything works as desired) and perform the following steps: You will re-configure your CAS2007 URLs in the "Internet Facing AD Site". This ensures that clients that leverage Autodiscover function correctly and that legacy mailboxes can be redirected to Outlook Web Access: Outlook Web Access: Set-OWAVirtualDirecotry \OWA* -ExternalURLhttps://legacy.contoso.com/owa Offline Address Book: Set-OABVirtualDirectory \OAB* -ExternalURLhttps://legacy.contoso.com/OAB Unified Messaging: Set-UMVirtualDirectory \UnifiedMessaging* -ExternalURLhttps://legacy.contoso.com/UnifiedMessaging/Service.asmx Web Services: Set-WebServicesVirtualDirectory \EWS* -ExternalURLhttps://legacy.contoso.com/ews/exchange.asmx ActiveSync: Set-ActiveSyncVirtualDirectory -Identity \Microsoft-Server-ActiveSync -ExternalURL https://legacy.contoso.com/Microsoft-Server-ActiveSync

The only question I see you asking is why a document doesn't include a step? I'm afraid nobody here knows the author and can answer that. If you have a question about the process, please post the complete and unadulterated command you issue and the complete error message you receive. Many of the commands and parameters you posted aren't correct so I can't make out where you might be having a problem. Also, in your subject you mention Exchange 2003, but in your text you say Exchange 2007. Please clarify that as well. Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."

Please refer this article if you are looking for Exchange 2003 /Exchange 2010 Co-existence.