Authentication errors processing Exchange Online backups

Update timeline

1. investigating Mar 27, 2026, 04:00 PM UTC

   Status: Investigating We are currently investigating an uptick in errors backing up Exchange Online mailboxes with the message “The HTTP request was forbidden with client authentication scheme ‘Anonymous’" with Microsoft. We will share additional information once we are able. More specific information is at https://www.veeam.com/kb4796. Affected components M365 - Asia Pacific (Partial outage) M365 - Europe, Middle East & Africa (Partial outage) M365 - Americas (Partial outage)

2. identified Mar 30, 2026, 07:21 PM UTC

   Status: Identified We have identified a mitigation for the Exchange Online backup authentication errors related to Exchange Web Services (EWS) access. Backups are succeeding for customers who enable EWS at both the organization and mailbox levels and allow time for Microsoft 365 replication to complete. We continue to work with Microsoft to investigate a small number of edge cases where issues may persist, and we will provide further updates as more information becomes available. More information on the workaround can be found here: https://www.veeam.com/kb479 "https://www.veeam.com/kb4796": https://www.veeam.com/kb4796 Affected components M365 - Europe, Middle East & Africa (Partial outage) M365 - Americas (Partial outage) M365 - Asia Pacific (Partial outage)

3. monitoring Apr 01, 2026, 09:38 PM UTC

   Status: Monitoring We continue to see successful backups for customers who have applied the configuration changes outlined in our knowledge base article. Customers who have not yet made these updates should follow the guidance in the article to restore normal backup operation. Please note, due to Microsoft 365 replication timing, it may take up to 24 hours after making these changes for backups to fully return to normal. We are not observing new widespread impact at this time. Knowledge base article: https://www.veeam.com/kb4796 Affected components M365 - Asia Pacific (Operational) M365 - Europe, Middle East & Africa (Operational) M365 - Americas (Operational)

4. resolved Apr 20, 2026, 09:56 PM UTC

   Status: Resolved We continue to see successful backups for customers who have applied the configuration changes outlined in our knowledge base article below. We have not observed any new recurrence of this issue. For remaining impacted customers, please refer to our Knowledge base article: https://www.veeam.com/kb4796 Affected components M365 - Asia Pacific (Operational) M365 - Europe, Middle East & Africa (Operational) M365 - Americas (Operational)