Microsoft has released Hotfix Updates (HUs) that enables support for new functionality and address issues in earlier updates.
- Exchange Server 2019
- Exchange Server 2016
HUs are available for the following specific versions of Exchange Server:
The April 2025 HUs do not contain any new Exchange Server security updates. We wanted to call out the following feature from this update:
Announcing Dedicated Exchange Hybrid Application
As a part of our Secure Future Initiative (SFI) we are making changes to improve the security of your Exchange Hybrid configuration. One of the steps toward this goal is to separate the identities of Exchange Server and Exchange Online by creating a dedicated Exchange hybrid application in Microsoft Entra ID. This is a part of our overall effort to deprecate legacy Exchange Web Services (EWS) API from Exchange Online and switch to using Graph API calls with granular Graph API permissions.
With the release of April 2025 HUs, we are ready to start the first step in this transition.
Exchange hybrid customers who require rich coexistence with Exchange Online must act between April 2025 HU release and October 2025. Unless you follow the steps to update to dedicated Exchange hybrid app (before October 2025) and then update it to Graph permission model (before October 2026), some Exchange hybrid functionality will break (Free/Busy sharing between on-premises and Exchange Online users, MailTips, profile picture sharing).
Please see the dedicated Exchange Server Security Changes for Hybrid Deployments blog post, the documentation and the FAQ related to the dedicated Exchange hybrid application and other related changes.
Known issues with this update
- Edge Transport service (EdgeTransport.exe) stops responding and then restarts when Exchanger Server attempts to decrypt the messages, sent from an external source protected by Azure Rights Management (Azure RMS).
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 HU will contain all the changes that a previous, older SU has. If you have not installed the older SU yet, you can install the newer HU directly and skip the older SU.
Our Exchange servers update automatically through Windows / Microsoft Update. Will our servers automatically install the HU update?
April 2025 HU will not be on Windows / Microsoft Update (this is not an indication of an issue with the update quality). We will resume release of updates there with the next upcoming update. Please download the April 2025 HU from the download center.
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.
Updates to this blog post:
- 5/21/2025 - changed the FAQ related to Windows / Microsoft update availability for April 2025 HU.
The Exchange Server Team
