Microsoft Releases Final Cumulative Update for Exchange Server 2019 – Here’s What’s New in CU15
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Microsoft announced the release of the 2025 H1 Cumulative Update (CU15) for Exchange Server 2019, marking the final cumulative update for this version. This release is significant as it not only introduces new features and fixes but also lays the groundwork for the upcoming Exchange Server Subscription Edition (SE).
Key Features and Changes
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Feature Flighting: CU15 introduces the server-side components for Feature Flighting, a new capability that will allow administrators to test and roll out select new features in their Exchange Server SE environment. This cloud-based service provides greater flexibility and control over feature adoption.
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Enhanced Diagnostic Data: CU15 includes the option to send additional diagnostic data to Microsoft, enabling the company to better understand and address issues related to flighted features.
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Support for Windows Server 2025: Both CU14 and CU15 support running Exchange Server 2019 on Windows Server 2025, ensuring compatibility with the latest server operating system.
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DocParser Integration: CU15 replaces Oracle Outside In Technology with DocParser, a Microsoft library designed to parse various file formats for Data Loss Prevention and Exchange Transport Rules.
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Partial TLS 1.3 Support: CU15 adds support for TLS 1.3 on Windows Server 2022 and later for all protocols except SMTP, enhancing security and performance.
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Improved AMSI Integration: CU15 incorporates the improved Exchange Server AMSI integration, bolstering the platform’s anti-malware capabilities.
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Certificate Management UI: The EAC now includes certificate management features, addressing a previous removal of these critical tasks.
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Coexistence with Exchange Server 2013 Blocked: CU15 cannot coexist with Exchange Server 2013, requiring the removal of all Exchange 2013 servers before installation.
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Extended Protection Enabled by Default: As a reminder, Extended Protection remains enabled by default after installation of CU15.
Preparing for Exchange Server SE
CU15 serves as a stepping stone to Exchange Server SE, with the RTM release of SE expected to be code equivalent to Exchange Server 2019 CU15. This approach ensures a smooth transition for customers upgrading from Exchange 2019.
Important Notes
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Customers in hybrid deployments or using Exchange Online Archiving with on-premises Exchange deployment must deploy CU15 for product support.
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CU13 is no longer supported, and customers are encouraged to update their servers to CU14 or CU15 as soon as possible.
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Microsoft plans to release an optional Hotfix Update (HU) for Exchange Server 2019 CU15 to address remaining bugs and maintain code parity with the RTM release of Exchange Server SE.
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