Exchange 2010 migration to Exchange 2016 coexistance - Outlook stops working

Question

Strange issue here. Started the migration to Exchange 2016 from a single server Exchange 2010 deployment, followed this six part techgenix guide https://techgenix.com/migrating-small-organization-exchange-2010-exchange-2016-part3/ (haven't decommissioned the old server as there are some old mailboxes that need to be archived) - everything seems to have gone well, but after migrating most of the users to the new databases on the 2016 server. A few of the users (so far) are complaining that after a period of time Outlook randomly stops sending their emails. Email will get stuck in the outbox, it will send if send/receive is pressed, but it won't be saved in the sent items folder, mail that was opened won't appear as read, autocomplete entries wont populate, etc.

Mail flow works perfectly through OWA, it seems to be an outlook connection issue. The test exchange connectivity website reports that autodiscover is working properly, however.

If they exit outlook and open again, it may enter the same state immediately or will work for a period of time before having issues again. It always reports that it's connected on the lower right, however.

Does anyone have any idea what could be happening?

Answer 1

Hi @Joey D ,

These events can be safely ignored because they don't adversely affect functionality and are by design. For more details: DCOM event ID 10016 is logged in Windows

For further troubleshooting, here are some troubleshooting steps you could refer to and narrow the issue:

• Could you run Test Email AutoConfiguration in outlook client and do there any error messages? Locate the Outlook icon in the notification area of the Start Bar and Ctrl+Left-click it. Select "Test E-mail AutoConfiguration.
  
• Try to recreate outlook profiles for the problematic users and check if this issue continues.
• Try to migrate one problematic usermailbox to another database, the migration process will repair the corrupted mailbox, and then check if this issue continues.

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Answer 2

I don't know if it's relevant but I'm seeing a ton of these errors in the event logs of the 2016 server. I also see dcom errors in the 2010 server.

Log Name: System
Source: Microsoft-Windows-DistributedCOM
Date: 4/13/2022 4:56:58 PM
Event ID: 10036
Task Category: None
Level: Error
Keywords: Classic
User: DOMAIN\LWSERVER11$
Computer: EX.domain.local
Description:
The server-side authentication level policy does not allow the user DOMAIN\LWSERVER11$ SID (S-1-5-21-537193806-524895414-1911729130-1014) from address 192.168.0.2 to activate DCOM server. Please raise the activation authentication level at least to RPC_C_AUTHN_LEVEL_PKT_INTEGRITY in client application.

Answer 3

Have you restarted the AutoDiscover App pool on he 2016 servers once the mailboxes are moved to 2016?

https://support.microsoft.com/en-us/topic/outlook-logon-fails-after-mailbox-moves-from-exchange-2010-to-exchange-2013-or-exchange-2016-bd3f59ed-c521-4349-5c00-c49717b5e04d