KB4913 release notes and known issues

Summary

Release Information for Veeam Backup for Microsoft 365 8.6 KB ID: 4913 Product: Veeam Backup for Microsoft 365 | 8.6 Published: 2026-09-14 Last Modified: 2026-09-14 Requirements This release can be used to: upgrade an existing v8, v8.1, v8.2, v8.3, v8.4, or v8.5 deployment of Veeam Backup for Microsoft 365 to v8.6. install a new deployment of Veeam Backup for Microsoft 365 v8.6. After installing this release, the Veeam Backup for Microsoft 365 build number will be 8.6.0.1102 . Release Information 8.6.0.1102 2026-09-14 Release Notes for Veeam Backup for Microsoft 365 8.6 New Features and Enhancements Added PowerShell cmdlets to remediate data in JET-based repositories, repositories with backup copies, and immutable repositories affected by the issue described in KB4835 . For more information, see KB4874 . When an organization is added or edited, the backup app registrations in Microsoft Entra ID automatically receive the permissions required to support Exchange mailbox protection after EWS retirement. For more information, see KB4820 . Added the ability to place object storage backup repositories into maintenance mode using PowerShell cmdlets or the REST API. While a repository is in maintenance mode, Veeam Backup for Microsoft 365 blocks all operations on that repository, allowing administrators to safely perform storage-level maintenance without interference. Bug Fixes General A retention task gets stuck and times out after the NATS server restarts. Backup and Backup Copy When the public folder hierarchy root stored in the backup no longer matches the root folder reported by Microsoft 365, public folder mailbox backup fails while processing the hierarchy root ( IPM_SUBTREE ) with the error: Object reference not set to an instance of an object In multi-geo organizations where location protection is disabled, SharePoint backup jobs fail with the error: Failed to resolve sites: ambiguous locations found SharePoint incremental backup jobs process all site changes from the beginning instead of continuing from the last backup point after SharePoint rejects a change token as outdated. When redirect site URL lookups are throttled and cannot acquire a request slot within the allowed wait time, even if throttling is not reported at the tenant level, a SharePoint backup job fails at the site resolution stage with the error: Request must be retried In organizations with a hybrid Exchange deployment, some mailboxes are skipped during backup with the warning: Exchange account was not found. A backup job that fails at the resolve stage because of Microsoft 365 throttling is reported as Failed. No restore point is created and no retry is attempted, even when some objects were processed successfully. A backup job processing SharePoint or Teams data does not trigger a retry run when all objects fail with the error: Access to this site is blocked. In multi-geo Microsoft 365 organizations, a throttling event in one geo region causes backup jobs in all other regions to slow down or fail. A Teams backup job fails with an out-of-memory error when processing channels that contain a very large number of messages. In multi-geo SharePoint environments, a backup job fails for sites whose data location cannot be resolved to any configured geo region. A SharePoint backup job intermittently fails during the resolve stage with the error: Object reference not set to an instance of an object When the backup scope includes archived Microsoft Teams, a backup job fails with the error: The response status code does not indicate success: 400 (Bad Request) Restore Browsing or restoring OneDrive and SharePoint data from archive-tier object storage hangs and eventually times out. Search in Veeam Explorer for Microsoft Exchange fails with an ArgumentOutOfRangeException error when a mailbox item contains an RTF-formatted body with emoji or other characters outside the Basic Multilingual Plane. Saving OneDrive items using Veeam Explorer for Microsoft OneDrive fails with

Improvements and security content

• Release Information for Veeam Backup for Microsoft 365 8.6 KB ID: 4913 Product: Veeam Backup for Microsoft 365 | 8.6 Published: 2026-09-14 Last Modified: 2026-09-14 Requirements This release can be used to: upgrade an existing v8, v8.1, v8.2, v8.3, v8.4, or v8.5 deployment of Veeam Backup for Microsoft 365 to v8.6. install a new deployment of Veeam Backup for Microsoft 365 v8.6. After installing this release, the Veeam Backup for Microsoft 365 build number will be 8.6.0.1102 . Release Information 8.6.0.1102 2026-09-14 Release Notes for Veeam Backup for Microsoft 365 8.6 New Features and Enhancements Added PowerShell cmdlets to remediate data in JET-based repositories, repositories with backup copies, and immutable repositories affected by the issue described in KB4835 . For more information, see KB4874 . When an organization is added or edited, the backup app registrations in Microsoft Entra ID automatically receive the permissions required to support Exchange mailbox protection after EWS retirement. For more information, see KB4820 . Added the ability to place object storage backup repositories into maintenance mode using PowerShell cmdlets or the REST API. While a repository is in maintenance mode, Veeam Backup for Microsoft 365 blocks all operations on that repository, allowing administrators to safely perform storage-level maintenance without interference. Bug Fixes General A retention task gets stuck and times out after the NATS server restarts. Backup and Backup Copy When the public folder hierarchy root stored in the backup no longer matches the root folder reported by Microsoft 365, public folder mailbox backup fails while processing the hierarchy root ( IPM_SUBTREE ) with the error: Object reference not set to an instance of an object In multi-geo organizations where location protection is disabled, SharePoint backup jobs fail with the error: Failed to resolve sites: ambiguous locations found SharePoint incremental backup jobs process all site changes from the beginning instead of continuing from the last backup point after SharePoint rejects a change token as outdated. When redirect site URL lookups are throttled and cannot acquire a request slot within the allowed wait time, even if throttling is not reported at the tenant level, a SharePoint backup job fails at the site resolution stage with the error: Request must be retried In organizations with a hybrid Exchange deployment, some mailboxes are skipped during backup with the warning: Exchange account was not found. A backup job that fails at the resolve stage because of Microsoft 365 throttling is reported as Failed. No restore point is created and no retry is attempted, even when some objects were processed successfully. A backup job processing SharePoint or Teams data does not trigger a retry run when all objects fail with the error: Access to this site is blocked. In multi-geo Microsoft 365 organizations, a throttling event in one geo region causes backup jobs in all other regions to slow down or fail. A Teams backup job fails with an out-of-memory error when processing channels that contain a very large number of messages. In multi-geo SharePoint environments, a backup job fails for sites whose data location cannot be resolved to any configured geo region. A SharePoint backup job intermittently fails during the resolve stage with the error: Object reference not set to an instance of an object When the backup scope includes archived Microsoft Teams, a backup job fails with the error: The response status code does not indicate success: 400 (Bad Request) Restore Browsing or restoring OneDrive and SharePoint data from archive-tier object storage hangs and eventually times out. Search in Veeam Explorer for Microsoft Exchange fails with an ArgumentOutOfRangeException error when a mailbox item contains an RTF-formatted body with emoji or other characters outside the Basic Multilingual Plane. Saving OneDrive items using Veeam Explorer for Microsoft OneDrive fails with

Affected products and versions

Recommended action

Review the official publisher document before deployment.

Official publisher evidence