Outlook 365 not autodiscovering on prem exchange after reinstall

Question

Summary : Outlook365 Autodiscover fails - Outlook 2019/2016 works fine with on-prem Exchange 2019.

I needed to rebuild a PC for a users to address an issue with another application. Windows 10 and Office 365 were reinstalled and since then Outlook 365 isn't locating the on-prem exchange 2019 server via Autodiscover. EXRCA testing shows Autodiscover is fine, and when Outlook 2016 or 2019 is used to establish the initial connection to a mailbox it works fine.

Any tips.

Answer 1

Hi @Shane King ,
Check whether on premise users enable the ExcludeExplicitO365Endpoint registry key under HKEY_CURRENT_USER\Software\Micrsoft\Office\16.0\Outlook\AutoDiscover.

If that doesn't work, use the Test E-mail AutoConfiguration tool to help determine why AutoDiscover failed in Outlook.

1. Start Outlook.
2. Hold down the Ctrl key, right-click the Outlook icon in the notification area, and then select Test E-mail AutoConfiguration.
3. Verify that the correct email address is in the E-mail Address box.
4. In the Test E-mail AutoConfiguration window, clear the Use Guessmart check box and the Secure Guessmart Authentication check box.
5. Select the Use AutoDiscover check box, and then select Test.

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