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We're currently running 2010 and 2016 in co-existence and we've migrated our first mailbox, woho!

However, on the test user account, the mailbox will not connect to the server, running an auto-discover test, we get prompted with a secondary logon for the user which always fails (see below)

Does anyone have any ideas?

Freddy Wetson
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2 Answers2

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According to the snapshot you post above, it looks like an Autodiscover action that Outlook uses a set of heuristics to determine whether the provided user account comes from Office 365. If Outlook determines confidently that you are an O365 user, an attempt is made to retrieve the Autodiscover payload from the known O365 endpoints(Outlook 2016 implementation of Autodiscover),

To avoid this action, you could try to add a DWORD value "ExcludeExplicitO365Endpoint" in the registry path "HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\x.0\Outlook\AutoDiscover", then restart Outlook to see the result. If it doesn't work, you could reboot this client to make the change valid.

Ivan_Wang
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There are several areas you need to check:

  1. Patch level of the clients.

  2. Patch level of servers, both 2010 and 2016.

  3. You need to match the authentication protocols between the servers. Run the following command to compare:

    Get-OutlookAnywhere | fl server, Name, URL, hostname, auth

  4. Make sure all client connections are pointing to the highest Exchange version.

  5. Validate that all virtual directories FQDN refer to Exchange 2016 environment, even those virtual directories defined on the Exchange 2010.

Vick Vega
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