Do you hate the new Outlook for Windows? An annoying bug causes the classic version to crash at launch, but Microsoft has issued a workaround

What you need to know

• Microsoft 365 users have flagged an annoying bug causing the classic Outlook app to crash at launch.
• The company acknowledged the issue caused by corrupted server-based rules for the M365 email account.
• While Microsoft works on a fix, it recommends deleting email rules linked to the affected accounts as a temporary workaround.

Over the past few days, several Microsoft 365 users have flagged an issue affecting the classic Outlook, causing it to crash. It occurred when trying to launch the app. Attempting to launch the app in Safe Mode also had a similar outcome.

Microsoft has acknowledged the issue and offered a workaround as it works on a fix to resolve it permanently. It can be characterized based on the details highlighted below:

You can confirm if this is the issue by looking at the Windows Event Viewer Application Log for crash Event 1000 or Event 1001, and the following event details:

Fault Bucket 1620625936954482602, Type 4
Faulting application name: OUTLOOK.EXE, version: 16.0.17830.20138, time stamp: 0x66aaad8c
Faulting module name: ucrtbase.dll, version: 10.0.22621.3593, time stamp: 0x10c46e71
Exception code: 0xc0000005
Fault offset: 0x000000000005137c
Faulting process id: 0x0x5A00
Faulting application start time: 0x0x1DAE741D3515015
Faulting application path: C:\Program Files\Microsoft Office\root\Office16\OUTLOOK.EXE

According to Microsoft:

"After updating to Version 2407 Build 17830.20138 or higher you find that Outlook may unexpectedly close at start up. Outlook will also close if you test in Safe Mode."

Microsoft has narrowed the issue to corrupted server-based rules for the M365 email account, preventing Outlook from processing them. While the company works on a permanent fix, it recommends manually deleting email rules linked to the affected accounts as a temporary workaround.

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How to delete Outlook's email rules manually

1. Close the classic Outlook app, right-click the Start button, select Run, and enter the Outlook.exe /cleanrules command line in the Run box to remove the client and server rules.
2. Press the Shift key when launching the app to create a new profile , if necessary.
3. If the issue persists, head to Outlook Web Access and manually remove all the email rules.

As you may know, the new Outlook for Windows shipped to broad availability. However, the app has been received with mixed feelings. The vast majority (arguably) have blatantly expressed their hate for the new app while citing their preference for the current built-in Mail & Calendar apps on Windows 10 and 11.

Users have listed several factors preventing them from transitioning to the new Outlook app, including lack of features, UI consistency issues, performance degradation, etc. Windows Central Senior Editor Zac Bowden says the new Outlook app is not ready for prime time , and Microsoft still has a lot of work to do.