Robert Hopman 1 Reputation point

Exchange 2010 and 2016 servers both running in an airgapped environment. Co-existence will not work properly (With DNS changed to point at the 2016 server 2010 mailbox users cannot get a proxied connection to their mailbox on 2010) Most users' mailboxes are still on 2010. We are using a recent version of Outlook 2016.

As as workaround, my plan is to make the DNS change to point at 2016 for mail and migrate our several hundred users a few nights at a time so as to not fill up on logs, etc. So, even though the down-proxying connection does not work for 2010 users, they can access OWA in the meantime to view critical messages (Not all users access this network regularly) With DNS changed, 2010 users are able to access 2010 OWA, and 2016 users are able to access 2016 OWA with no issue

Issue I'm facing right now is that with DNS still pointing to Exchange 2010, any user that has a mailbox on the 2016 server cannot access OWA and gets the following error:

Server error in '/OWA' Application

Unhandled execution error

Exception details Microsoft.Exchange.Clients.Owa.Core.WrongCASServerBecauseOfOutOfDateDNSCacheException

Microsoft.Exchange.Clients.RequestDispatcher.SetRedirectDestinationUrl(OwaContext owaContext) +1319 Microsoft.Exchange.Clients.RequestDispatcher.PrepareRequestWithoutSession(OwaContext owaContext, UserContextCookie userContextCookie) +712 Microsoft.Exchange.Clients.RequestDispatcher.AcquireAndPreprocessUserContext(OwaContext owaContext, HttpRequest request) +786 Microsoft.Exchange.Clients.RequestDispatcher.InternalDispatchRequest(OwaContext owaContext) +836 Microsoft.Exchange.Clients.RequestDispatcher.DispatchRequest(OwaContext owaContext) +86 Microsoft.Exchange.Clients.OwaRequestEvetInspector.OnPostAuthorizeRequest(Object sender, EventArgs e) +285 System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +80 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +171

I made sure that the dns cache was flushed on the workstation I was testing on and both 2010/2016 servers - cleared browser data, etc.

Any help is appreciated.

Exchange Server Management
Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
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  1. Kael Yao-MSFT 37,586 Reputation points Microsoft Vendor

    Hi @Robert Hopman

    Issue I'm facing right now is that with DNS still pointing to Exchange 2010, any user that has a mailbox on the 2016 server cannot access OWA and gets the following error

    I suppose it is the expected behavior, as Exchange 2010 cannot up-proxy to Exchange 2016.
    While Exchange 2016 can down-proxy to Exchange 2010.

    In this case, you may need to set the DNS records to point to Exchange 2016 server.

    In addition, for the whole migration process, it is recommended to use the exchange deployment assistant tool.
    It would contain all the required steps about migration.

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