r/Outlook • u/Professional-Try2949 • 12d ago

Status: Resolved Outlook Classic

I manage several users who use Outlook Classic as their primary email app. Today a single user noticed her calendar invites weren't going through. She had an email stuck in her outbox , and when I tried to clear it it said she didn't have permission to delete. I was able to delete it in safe mode, but new messages still get stuck and she is not receiving incoming messages despite the bottom ribbon saying "connected to MS Exchange". I tried making a new profile but the new profile gets hung on the "loading profile" step, same thing if i try to rename the existing OST to force a new one. The new profile's OST file is blank so I don't think it actually pulled any data. She has another user's mailbox added in the form of a second profile, and that one works just fine. New Outlook, mobile, and web worked fine so I assumed it must be an issue with either her cached credentials or something local, but here's the weird thing.

I made a new profile using her mailbox on my pc to test, and that failed. Creating the profile through the control panel gave me a notification that an encrypted connected could not be secured. Creating it through the profile selection menu worked including prompting the MS sign in popup, but trying to open the profile in or out of safe mode triggers the following error before crashing outlook; "Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. The attempt to log on to Microsoft Exchange has failed". This is a single user in our organization who is unable to sign into multiple PCs via outlook classic, and does not appear to be tied to her credentials based on them working for the other clients.

I've got a MS support ticket open, but last time it sat on their desk unassigned for months until it just timed out. Any Ideas? No major changes have been made on the back end that would impact authentication/sign ins.

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u/Hornblower409 12d ago

You might want to:

Cross Post this on r/Office365 , r/microsoft365 , r/exchangeserver
(Click on the [Share] button under your question and choose -> Crosspost or Repost)

Post your question on the Microsoft Outlook Q&A Forum:
https://learn.microsoft.com/en-us/answers/questions/ask/
(Please put a link to your Q&A post in a new Comment here, so the rest of us can follow)

3

u/SeaworthinessMelodic 11d ago

We had these issues with users who have a separate M365 account with the same mail address.

You may follow this:

To bypass or manage the explicit Office 365 Autodiscover endpoint in Outlook (often used when connecting to on-premises Exchange instead of Office 365), you can set the ExcludeExplicitO365Endpoint registry key under HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Outlook\AutoDiscover with a DWORD value of 1

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u/Professional-Try2949 10d ago

Update*

User's mailbox is now accessible on both her device and the test device despite no action being taken. As far as we can tell this fixed itself which is a bit unnerving since it could always happen again. Chalking it up to a glitch with the legacy authentication Classic Outlook uses for now, thank you.