Microsoft Rolls Out September 2026 Exchange Server Hotfix Updates

Microsoft has released September 2025 Hotfix Updates (HUs) for Exchange Server, addressing non-security issues that impacted some hybrid deployments. The update covers Exchange Server Subscription Edition (SE), Exchange Server 2019 CU14 and CU15, and Exchange Server 2016 CU23.

Unlike security updates, these hotfixes are not tied to Patch Tuesday. Microsoft explained that the early release was necessary after hybrid customers reported problems while deploying the dedicated Exchange hybrid app, first introduced with the April 2025 HUs.

The update provides fixes but does not include any new security patches. Microsoft reminds admins that since all Exchange updates are cumulative, installing the September HU automatically applies past fixes as well.

Admins can use the Exchange Server Health Checker script to determine if updates are required, followed by the Exchange Update Wizard for installation guidance. If errors appear, Microsoft recommends running the SetupAssist script or referring to documentation such as Fix failed Exchange Server updates.

The HUs are available through Windows Update, depending on organizational deployment policy, and can also be uninstalled if necessary. Microsoft confirmed that all features and fixes included in this HU will be carried forward into future updates.