[German]A quick question for users and administrators who are still using Microsoft Outlook 2019 (support for Office 2019 expired in October 2025). I've received a report that it's currently no longer possible to connect to Exchange Online mailboxes. There have also been reports that Outlook 2021 and Outlook 2024 LTSC—and possibly Outlook 365 as well—may be affected. However, there is a workaround that seems to be helping those affected.
Blog reader Michael emailed me this morning with the subject line "Outlook 2019 no longer connects to O365 / Exchange Online" to bring this issue to my attention. There appear to be issues establishing a connection from Microsoft Outlook to Exchange Online mailboxes. Michael sent me a link to the Reddit.com post "office 2019 not connecting to exo mailboxes" from March 18, 2026.
In the post, an affected user asks whether other users are also experiencing the problem where Outlook cannot connect to Exchange Online mailboxes. The authentication animation "just spins endlessly in a circle" for the user. The poster writes that he knows support for Microsoft Office 2019 has already expired. However, it was still working as of the morning of March 18, 2026. He states that he just hasn't migrated all systems to the Microsoft 365 apps yet.
In replies to the post, other users confirm that there are issues with Outlook 2019, as well as with Office 2021 LTSC. According to user reports, the latter causes problems when opening Outlook. Connection issues with Microsoft 365 apps—and presumably Outlook 365—were also reported in the thread.
One user writes that they were able to find a workaround for this connection issue. To do this, the following commands must be saved to a .reg file and then imported using the Registry Editor or by double-clicking the file.
[HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity] "DisableAADWAM"=dword:00000001 "DisableADALatopWAMOverride"=dword:00000001 "EnableAdal"=dword:00000001
The registry entries listed above disable the Windows Web Account Manager (WAM) for Microsoft Entra ID. This enables authentication via the Azure Active Directory Authentication Library (ADAL). Based on the comments on reddit.com, this change seems to resolve the connection issue for some users. Has anyone else experienced this problem?
Within my German blog post, somebody left the following comment, which I've translated to English.
I can also confirm this issue with Office 2024 LTSC. We are using an expired Exchange 2019 (without SE), and I found an Exchange Server without IIS installed. I was also unable to access Internet Information Services Manager in Server Manager.
I was able to open the MMC via cmd and access the IIS plugin, but IIS was missing a certificate on port 444. After I stopped the IIS service on Exchange and assigned the current certificate via "Bindings," the Exchange Server started working again.
But I suppose, that the above approach doesn't help for Exchange Online postboxes.
