On Exchange 2016 (Version 15.0 ‎(Build 847.32)‎) we have a single mailbox that is used on 2 computers. When computer A has Outlook 2010 open, computer B can no longer open Outlook 2010. However, the exact opposite happens when you open Outlook on computer B first. Then computer A gets the error message. The computers are stand alone and are logging in with the same domain account. However, I tried using different AD accounts and the issue persists.

Error message when trying to open Outlook while the mailbox is opened on the other computer: "Cannot open default email folders, Microsoft Exchange is not available" However it is possible to ping the server (IP and DNS) and ping autodiscover.domainname.com

Already tried to:
- Set Maximum concurrent connections to unlimited
- Set Maximum concurrent connections per domain to unlimited
- Remove the profile on both computers
- Restarted the Exchange server and computers
- Removed all ost files under C:\Users\%username%\AppData\Local\Microsoft\Outlook

  • Are you using the same AD account or are there two different accounts used (e.g. one for PC 1 and one for PC 2). Did you tried using the Outlook Cache mode? Are these real PCs or some kind of terminal server? – BastianW Oct 30 '17 at 20:03
  • I updated my question: It are standalone computers and they are using the same AD account to log in. – user2827958 Oct 31 '17 at 8:46
  • Update: Using different AD accounts does not resolve the issue. – user2827958 Nov 6 '17 at 14:37

There are multiple areas that needs to be validated:

  1. Appropriate version of Outlook 2010. In order to connect to Exchange 2016 it needs to be: Outlook 2010 SP2 and updates KB2956191 and KB2965295 See here.

  2. You seems to be running CU5, probably should upgrade to CU6 or CU7. See here.

  3. On the internal network, in order to get to the CAS, SCP is used. Let's see the results of:

    Get-ClientAccessService | fl Name,OutlookAnywhereEnabled, AutodiscoverServiceInternalUri

  • Updating to CU7 resolved this issue. Thank you. – user2827958 Nov 24 '17 at 6:54

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