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Microsoft has released Hotfix Updates (HUs) that address issues in earlier updates for:

• Exchange Server 2019


• Exchange Server 2016

HUs are available for the following specific versions of Exchange Server:

• Exchange Server 2019 CU14 and CU15


• Exchange Server 2016 CU23

The May 2025 HUs do not contain any new Exchange Server security updates but contain fixes for non-security issues. Please see the release KB article for more information.

Because it has been listed as a “known issue” during a few recent releases, we wanted to call out that one of the issues addressed in this HU is Edge Transport service stops responding after installing November 2024 SU.

Reminder: Dedicated Exchange Hybrid Application support

We wanted to remind you that since our updates are cumulative, May 2025 HUs include support for creation of dedicated Exchange hybrid app originally released in April 2025 HU. Please see our April 2025 HU announcement as well as feature documentation and FAQ.

Update installation

The following update paths are available:

• Inventory your Exchange Servers to determine which updates are needed using the Exchange Server Health Checker script. Running this script will tell you if any of your Exchange Servers are behind on updates (CUs, SUs, or manual actions).


• Install the latest CU. Use the Exchange Update Wizard to choose your current CU and your target CU to get directions.


• Re-run the Health Checker after you install an update to see if any further actions are needed.


• If you encounter errors during or after installation of Exchange Server, run the SetupAssist script. If something does not work properly after updates, see Repair failed installations of Exchange Cumulative and Security updates. Also please see File version error when you try to install Exchange Server updates.

Hotfix Update FAQs

We installed the last Security Update. Should we install the later Hotfix Update?
Exchange Server HUs are optional updates, but they might introduce features or fixes that your organization can benefit from. Please see the release KB article for more details.

We did not yet install the earlier Security Update. Do we have to install the last available SU first before installing the later HU?
All of Exchange updates (HUs or SUs) are cumulative. Therefore, a newer SU or HU will contain all the changes that a previous, older SU or HU has. If you have not installed the older updates yet, you can install the newer one directly and skip the older one.

Our Exchange servers update automatically through Windows / Microsoft Update. Will our servers automatically install the HU update?
HUs will appear as an optional update for your servers. The update will also be available on the Microsoft Update Catalog after a few days of delay.

Will the new features and fixes released in the HU also be rolled into future updates, or must we install this specific HU to get them?
Content of this HU will be included in subsequent updates for Exchange Server.

Can HUs be uninstalled (if the need arises)?
Yes. HUs, like SUs, can be uninstalled.

Documentation may not be fully available at the time this post is published.

This post might receive future updates; they will be listed here (if available).

The Exchange Server Team