Exchange Server 2019 Cumulative Update H1 2025 (CU15) Released
Microsoft has released the highly anticipated 2025 H1 Cumulative Update (CU15) for Exchange Server 2019. This marks a significant milestone as it will be the final cumulative update for Exchange Server 2019 before it reaches end-of-life in October 2025.
Key Features and Changes
Feature Flighting
Exchange 2019 CU15 introduces server-side components for Feature Flighting, a new capability designed for mailbox servers. This optional cloud-based service will enable administrators to test and roll out select features across their Exchange Server SE organization. The service utilizes the Office Config Service (OCS) for checking updates from Microsoft.
Windows Server 2025 Support
Both CU14 and CU15 now support running Exchange Server 2019 on Windows Server 2025, including environments with Active Directory servers running Windows Server 2025. This enables organizations to install either version on new hardware with Windows Server 2025 and later upgrade to Exchange Server Subscription Edition (SE).
Security and Protocol Improvements
- Partial TLS 1.3 support for Windows Server 2022 and later (except SMTP)
- Integration of all security changes from November 2024 SU v2
- Fix for the known time zone issue from November 2024 SU
Technical Enhancements
DocParser Implementation
Microsoft has replaced the Oracle Outside In Technology with DocParser, a Microsoft library designed for parsing various file formats. This new implementation handles text extraction for Data Loss Prevention and Exchange Transport Rules.
Certificate Management
The Exchange Admin Center (EAC) now includes the previously removed certificate management functionality, restoring critical certificate management tasks.
Exchange SE In-place Upgrade Support
Exchange 2019 CU15 is required to provide a migration path to the next-generation Exchange Server SE (Subscription Edition).
Important Notes for Administrators
Compatibility Requirements
- Exchange Server 2019 CU15 cannot coexist with Exchange 2013 servers
- Extended Protection remains enabled by default since CU14
Diagnostic Data Collection
CU15 introduces additional diagnostic data collection capabilities, which will be sent to Microsoft when enabled by administrators.
Future Roadmap
The release of CU15 paves the way for Exchange Server Subscription Edition (SE). Microsoft has delayed some features, including Exchange Server SE product key support, until Exchange Server SE CU1 to ensure smooth in-place upgrades. Organizations running Exchange Server 2019 should plan their upgrade path carefully, as support for Exchange Server 2019 will end on October 14, 2025. Microsoft recommends upgrading to CU15 to facilitate a seamless transition to Exchange Server SE when it becomes available.
Microsoft recommends that all customers test the deployment of an update in a lab environment to determine the proper installation process for their production environment.
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