EWS 403 Errors Due To Graph Scream Tests

10 September 2026

Exchange Online EWS 403 Errors

Exchange Online EWS 403 errors are currently occurring due to Microsoft's randomized "scream tests" designed to identify hidden dependencies before the final October 1, 2026 shutdown of Exchange Web Services.  These tests temporarily disable EWS access for approximately 50% of mailboxes randomly, regardless of individual mailbox configurations or permissions. 

Solution

To prevent disruption, tenants must proactively enable EWS via PowerShell by running Set-OrganizationConfig -EwsEnabled $true.  This tenant-level setting exempts the organization from these temporary disable cycles, though changes may take 15–30 minutes to propagate. Full details of this process can be found in the Forms Printer Knowledgebase Article here: Extend Use Of EWS Until April 1, 2027

Organizations relying on EWS can alaso avoid the issue by migrating to Microsoft Graph API. Details of the migration process can be found in the Forms Printer Knowledgebase Article here: Switch To Microsoft Graph From EWS