Cannot launch Outlook 365 offline - "the set of folders cannot be opened"

Question

Windows 10 21H2 (OS Build 19044.1706)
Office 365 2204 (Build 15128.20178)

I'm unable to launch Outlook 365 offline. I get the error: "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." Once Outlook has started and successfully connected, I can then go offline, but if I am not online during launch I can never get in.

I've tried:

• starting in safe mode
• sfc /scannow
• dism /online /cleanup-image /checkhealth
• creating a new profile
• creating a new C:\Users...\appdata\local\Microsoft\Outlook folder
• toggling cached exchange mode on and off
• toggling "turn on shared calendar improvements"
• disabling "download shared folders" in advanced account settings
• disabling "favorites" in the folder pane
• creating a registry REG_DWORD key HKCU\Software\Microsoft\Office\16.0\Outlook\AutoDiscover\ExcludeScpLookup with Value 1

None of these change the behavior.

Any ideas?

Answer 1

Hi @AdamKessel-0270 ,

Welcome to our forum!

Glad to know that your issue is resolved now! Since our forum has the policy that The question author cannot accept their own answer. They can only accept answers by others, and according to the scenario introduced here: Answering your own questions on Microsoft Q&A

I would make a brief summary of this post so that other forum members could easily find useful information here:

[Activating lagged copies - Summary]

Issue Symptom:
Cannot Open Outlook365 When Offline

Solution:
Set created key in HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover
DWORD ExcludeExplicitO365Endpoint = 1

Reference Links:
How to Prevent Outlook in Connecting to Office365 Account

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You could "Accept Answer" for this summary to close this thread, and your action would be helpful to other users who encounter the same issue and read this thread. Thanks for
your understanding!

Answer 2

Found a fix! Set created key in HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover

DWORD ExcludeExplicitO365Endpoint = 1

Now I can start offline. As a bonus, Outlook also launches much faster.