Originally we had the following setup: OfficeExch01 has Mailbox Role and CAS Role OfficeExch01 is in the office. CoLoExch01 had just CAS Role. CoLoExch01 is internet facing and in a CoLo. Three AD domain controllers in the default site. Users could go to https://webmail.whatever.com/owa, get proxyed to OfficeExch01 and everything was great. Well, we recently setup a separate AD site and put a domain controller and the ColoExch01 server in the new site. I also made that remote DC be a Global Catalog. Now, users get the following error: Outlook Web Access is not available. If the problem continues, contact technical support for your organization and tell them the following: There is no Microsoft Exchange Client Access server that has the necessary configuration in the Active Directory site where the mailbox is stored. I also see event 41 errors in the logs: The Client Access server "https://webmail.xxxxxxx.com/owa" attempted to proxy Outlook Web Access traffic for mailbox "/o=XXXXX/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=xxxxxxk". This failed because no Client Access server with an Outlook Web Access virtual directory configured for Kerberos authentication could be found in the Active Directory site of the mailbox. The simplest way to configure an Outlook Web Access virtual directory for Kerberos authentication is to set it to use Integrated Windows authentication by using the Set-OwaVirtualDirectory cmdlet in the Exchange Management Shell, or by using the Exchange Management Console. If you already have a Client Access server deployed in the target Active Directory site with an Outlook Web Access virtual directory configured for Kerberos authentication, the proxying Client Access server may not be finding that target Client Access server because it does not have an internalUrl parameter configured. You can configure the internalUrl parameter for the Outlook Web Access virtual directory on the Client Access server in the target Active Directory site by using the Set-OwaVirtualDirectory cmdlet. Looking this up I see a lot talk about ExternalURL and InternalURL settings. However, everything worked great until we made the new AD site. I also made sure the internal CAS server's /owa virtual directory is set to use Integrated Authentication. Is there something I need to do to allow Exchange to see that I've made these AD changes?