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GreggHamby-0591 asked KaelYao-MSFT edited

Exchange 2016 post migration issue with Outlook 2019

Greetings all. I'm wrapping up a migration from on-prem Exchange 2010 to on-prem Exchange 2016. Specs are below: Exchange 2016 CU 18 Outlook 2016 Pro Plus 16.0.5134.100 32-bit Outlook 2019 Pro Plus 1808 10372.20060 64-bit We tried and failed to move public folders using the migration scripts. In terms of Outlook client functionality everything appeared fine up to that point. We then deleted the existing public folder deployment from 2010 and created a new empty structure on Exch 2016. The client then started importing everything in from PST which was also working fine. Weirdly, we observed that as soon as the new PFs came live on 2016 all of the Outlook 2019 clients started prompting for a password upon connection. The 2016 Outlook clients are fine. OWA is fine. When the Outlook 2019 user connects and is prompted all they have to do is click on the "Need Password: prompt at the bottom at which point the dialog goes away and they can work fine. Then at some point - 10m, 1 hr, 2hrs? - the prompt will reappear. We have tried everything from blowing away the profile, logging in on a new machine with a new profile, checking the RCP stats - everything looks normal and shows the Outlook 2019 users connected to the new single Exchange 2016 server. Any help would be greatly appreciated. Thanks.

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Hi,@GreggHamby-0591

Agree with Andy, it may be caused by the new feature in Outlook 2016 version 16.0.6741.2017 or later versions, which tries to connect to O365.
And since Outlook 2016 16.0.5134.100 is a legacy version, it isn't affected.

To resolve the problem, you may follow these steps:
1.open Registry on the client device and locate "HKEY_CURRENT_USER\Software\Microsoft\Office\x.0\Outlook\AutoDiscover"
2.add a new DWORD(32-bit) value named ExcludeExplicitO365Endpoint and set its value to 1
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3.restart Outlook and check if the problem persists

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1 Answer

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AndyDavid answered KaelYao-MSFT commented

Could be the 2019 clients are actually trying to contact Office 365:
You can fix with a registry fix;
https://medium.com/jj365/outlook-issue-with-direct-connect-to-office365-352dd29de65



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Thanks guys. This indeed turned out to be the issue. The customer thought they had tried this earlier but must have applied it incorrectly.
I have to vent a little - this customer has been running 2019 in their environment for a year. The problem only manifested itself upon installation of a 2016 Exchange server. While 2010 was the primary server they never observed this.

Kael - you're with MS? So is this the official answer? "Just go perform a reg hack to 1000 systems on your campus and we're all good?" This customer is on prem but is dealing with this issue because - apparently - MS will see you in the cloud or you can die trying to remain on prem.

I thank you both for your answers.

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Hi,

While 2010 was the primary server they never observed this.
Since this issue is caused by the new feature of Outlook, and there are some cases in the similar situation with Exchange server 2010, I am not sure why it works fine before.

"Just go perform a reg hack to 1000 systems on your campus and we're all good?"
Sorry for the inconvenience.
While since it is caused by the feature of Outlook, there is no way to resolve the issue on the server side.
As a workaround,you may need to create a GPO to modify the registry on the user devices.

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