Outlook does not connect using MAPI

Hi Андрей Михалевский,

Thank you for posting your question in the Microsoft Q&A forum.

In general, Outlook uses Autodiscover service to obtain configuration information for Exchange server, then could connect Exchange with MAPI/HTTP.

Based on your description, “If I select - configure manually and select Exchange - Outlook is configured via MAPI”, do you mean you have to choose the mailbox type and Outlook could setup successfully?

If so, it seems that Exchange Autodiscover service still works. Here are some suggestions and information for further troubleshooting:

1. Do you have pure on-prem Exchange server environment, or have Exchange Online and add the domain in M365? Outlook may retrieve the Autodiscover payload from the known O365 endpoints. If you have O365 in your organization, this could cause O365 login page prompts up for your on-prem Exchange mailbox or Autodiscover may fail if something else interrupt the process. You can check this article for more information about Outlook Autodiscover: Outlook 2016 implementation of Autodiscover - Microsoft Support 
2. You can try the following registry value to prevent Outlook from checking for O365 as priority. Important: Follow the steps in this section carefully. Serious problems might occur if you modify the registry incorrectly. Before you modify it, back up the registry for restoration in case problems occur.
   1. Open the Registry Editor by typing regedit in the Windows Search or open the run and type regedit.exe.
   2. Find this location below in the regedit: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover
   3. Create a DWORD (32-bit) value for ExcludeExplicitO365Endpoint and change the value to “1” to enable it.
   4. Then close Registry Editor and reopen Outlook to setup mailbox.

For more details, please check: Unexpected Autodiscover behavior if settings under the \Autodiscover key | Microsoft Learn 

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Disable Modern Auth fixed my problem:

New-Item -Path "HKCU:\Software\Microsoft\Office\16.0\Common\Identity" -Force

Set-ItemProperty -Path "HKCU:\Software\Microsoft\Office\16.0\Common\Identity" -Name "EnableADAL" -Value 0 -Type DWord

Set-ItemProperty -Path "HKCU:\Software\Microsoft\Office\16.0\Common\Identity" -Name "DisableADALatopWAMOverride" -Value 1 -Type DWord

But I can't figure out the cause and can't find documentation to explain how this is related

Hi Андрей Михалевский,

Glad to hear this issue has been resolved, and much appreciation for your sharing!

Based on your reply, your issue may be related to some Microsoft 365 sign-in or activation issue and disable ADAL and WAM make it work again. Here are some similar issues for your reference:

Disabling ADAL or WAM to fix Microsoft 365 sign-in or activation issues not recommended - Microsoft 365 | Microsoft Learn 

Modern Auth Looping with Outlook 2016 when Outside Corporate Network | Microsoft Community Hub 

However, due to the forum policy update, the author of the question is now unable to accept his/her own answer. Therefore, I have written a short summary of how to solve this problem. Please accept it as an answer so that others who are going through the same thing can more easily refer to this.

Issue:

We have installed Windows 11 and Office LTSC 2024 Pro Plus. Use Exchange 2019 - last cu, su and Outlook 2408(17932.20286).

1. Outlook classic does not connect automatically to mapi, it thinks for a long time and offers to connect via IMAP.
2. If I select - configure manually and select Exchange - Outlook is configured via MAPI.
3. Outlook connection check shows success on all protocols.

Also, we installed Office 2021 and Outlook automatically connects to mapi.

The computer is in a domain. License activated for office and OS. For some reason only this version of Outlook does not work in our organization.

Solution:

Disable Modern Auth:

New-Item -Path "HKCU:\Software\Microsoft\Office\16.0\Common\Identity" -Force

Set-ItemProperty -Path "HKCU:\Software\Microsoft\Office\16.0\Common\Identity" -Name "EnableADAL" -Value 0 -Type DWord

Set-ItemProperty -Path "HKCU:\Software\Microsoft\Office\16.0\Common\Identity" -Name "DisableADALatopWAMOverride" -Value 1 -Type DWord

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