Exchange Autodiscover for multi-forest disjoint namespace

This is on Exchange 2010/2013 with Outlook 2010. has merged with to form Each company (A & B) has its own AD Forest, and its own separate Exchange server with its own users/mailboxes. These users now have a new default email address (that part has been configured fine). The problem is that Outlook tries to "autodiscover" the default email address ( and the mailboxes sit on two separate Exchange servers that know nothing about each other. Is there a way I can configure autodiscover so that users are "redirected" to the correct server? I do not want to user local XML files or do anything that requires changes to the client computers, I am looking for a solution that I can setup on the server side. Thanks!
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Simon Butler (Sembee)ConsultantCommented:
There is no server side solution that I am aware of.
Obviously internally it isn't a problem, as the clients will query the domain for the information, but externally there is no mechanism for Exchange to redirect users to another server.
Therefore client side is your only option, almost certainly using an alternative URL than


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Will SzymkowskiSenior Solution ArchitectCommented:
In situations like this I have also told that client to use a common namespace externally that ALL users will use. This is only for External access. Aside from that I agree with Simon there is no other way to accomplish this externally.

criskritAuthor Commented:
Hello guys and thanks for the answers. I feared there is no solution. Will, what do you mean by common external namespace? Obviously I can setup to point to an IP but the problem is distributing the users afterwards. Thanks.
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Will SzymkowskiSenior Solution ArchitectCommented:
If you have your Exchange environment setup where there is one entry point you can setup multiple smpt domains (accepted domains) and or external relay domains. This way you only have to manage 1 entry point and then everyone connects using the same external

As you have currently stated in your initail question that you have 2 separate forests so there would be some work involved to get this working properly but it has to go to 1 common external dns name. From there you then Relay the email to another Exchange environment or create accepted domains and host the mail on the same server.

criskritAuthor Commented:
Email relay & flow is fine the problem is autodiscover. Autodiscover has to send some users to Exchange/Forest A and some users to Exchange/Forest B. Is this possible? If I setup autodiscover to point to ie Exchange/Forest A, is there a way to redirect users from there to Exchange/Forest B in the event that they are not found on the first server? Thanks.
Will SzymkowskiSenior Solution ArchitectCommented:
What you are specifically asking for is not possible for autodiscover. DNS has no intelligence to be able to decipher where connections should be going.

Unfortunately what you are trying to accomplish is not possible.

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