How to fix the issue when Outlook won’t find Office 365 mailbox because there is an on-premise Microsoft Exchange server or legacy domain controller; often this issue will happen after performing an on-premise Exchange to Office 365 migration.
So, after migrating everything over and shutting down the Exchange server I ran into the issue that Outlook would get hijacked by active directory and autocomplete or autodiscover the user’s AD and Exchange information and not allow us to input our Office 365 mailbox credentials
Until you uninstall Exchange, AD will often hijack your Outlook profile and try to sync your Exchange email profile instead of your Office 365 account
Newer version of Microsoft Outlook should get around this issue but if you have Microsoft Office 2016 or earlier you may experience these issues
The easy fix is to change the DNS server on the computer trying to connect to Office 365 to 8.8.8.8 and then change it back after it connects but we understand that this won’t always work
Add these 2 registry entries to try and work around the Exchange issue as well:
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Common\Identity\EnableADAL (set Value to 1)
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Outlook\AutoDiscover\ExcludeHttpsRootDomain (set value to 1)
After much testing and googling this is how to get Outlook to connect to our Office 365 mailbox when you still have an AD Connected Exchange Server (it’s not my prettiest solution but it works until you can uninstall your Exchange server):
- I had to install the Office 2016 Group Policy template located here
- I copied the extracted ADMX and ADML files to GP store on my server 2012 (this will be dependent on your server or PC’s OS)
- I opened up Group Policy Management created a GPO and linked it to my domain
- In the GP I went to \user\policies\admin templates\Outlook 2016\accounts settings\exchange\ and then enabled “disable auto discover‘
- Within that same GP setting, I enabled all the excluded settings
- In IIS Manager on the Exchange Server, I disabled the MSExchangeAutodiscoverAppPool and set it to not auto-start
- This last part may be the weirdest and may actually be the only thing I needed to do but it was so far down the road that I couldn’t test it as a stand-alone solution, we had to remove all existing outlook profiles and then open Outlook (not MAIL) and create a brand new profile from scratch.
- When the profile is being set up I had to choose the option to sign in with a different account, do a manual setup and then enter the O365 mailbox in the field and it finally connected
Ultimately, your best bet for having this work correctly is to remove the Exchange Server roles from your network but we understand that sometimes that is not possible.
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