Microsoft Outlook Error 440

Solution I found was to clear the Outlook localState to restore Outlook web functionality

Steps to solve this problem

1. Close web browser.
2. Open Command Prompt with Administrator’s rights.
3. Navigate to
   
   C:\Program Files\WindowsApp\Microsoft.OutlookForWindows_1.2024.717.400_x64__8wekyb3d8bbwe
   
   
4. Execute the following
   
   olk.exe --clearLocalState
   
   
5. Open web browser and navigate to https://outlook.office365.com/.
6. Login and your Outlook web should be back to normal.

References:

https://answers.microsoft.com/en-us/outlook_com/forum/all/troubleshoot-regard-try-new-outlook-outcome/0a5adf43-2f55-4c6f-acb5-b59634a87396