In a significant development for IT infrastructure, Microsoft has released the final Cumulative Update (CU15) for Exchange Server 2019, marking the culmination of its support for this version. This update, which became available on February 10, 2025, introduces several new features, security enhancements, and compatibility updates, while also laying the groundwork for the forthcoming Exchange Server Subscription Edition (SE).

Background and Context

Exchange Server 2019 has been a cornerstone for many organizations, providing robust email and calendaring solutions. Microsoft had initially planned to release CU15 in the second half of 2024. However, due to unforeseen issues discovered during the Technology Adoption Program (TAP) testing phase, the release was postponed to early 2025. This delay underscores Microsoft's commitment to delivering a stable and secure product. (techcommunity.microsoft.com)

Key Features and Enhancements in CU15

CU15 introduces several notable features and improvements:

  • Feature Flighting: This new capability allows administrators to test and roll out select new features in Exchange Server SE without requiring a dedicated test environment. It leverages the Office Config Service (OCS) for update management and enables Microsoft to disable problematic features if necessary. Feature Flighting is optional but enabled by default and will apply only to future updates; no features are currently flighted in CU15 or Exchange Server SE RTM. (redmondmag.com)
  • Partial TLS 1.3 Support: CU15 introduces support for TLS 1.3 on Windows Server 2022 and later for all protocols except SMTP. When CU15 is installed on Windows Server 2022 or later, TLS 1.3 is enabled by default, enhancing security by eliminating obsolete cryptographic algorithms. (borncity.com)
  • Enhanced AMSI Integration: The Advanced Malware Scanning Interface (AMSI) integration has been improved, bolstering the server's ability to detect and mitigate malware threats. (borncity.com)
  • Reintroduction of Certificate Management in EAC: CU15 brings back critical certificate management tasks to the Exchange Admin Center (EAC), streamlining administrative processes. (borncity.com)

Implications and Impact

The release of CU15 signifies the end of support for Exchange Server 2019, with the product reaching its end-of-life on October 14, 2025. Organizations are encouraged to migrate to Exchange Server SE or consider cloud-based solutions like Exchange Online to ensure continued support and access to the latest features. The delay in CU15's release has provided administrators with additional time to plan and execute these transitions effectively. (messageware.com)

Technical Details

CU15 is designed to be code-equivalent to the upcoming Exchange Server SE RTM release, facilitating a smoother upgrade path for organizations transitioning to the new edition. Notably, CU15 supports Windows Server 2025, allowing organizations to deploy Exchange on new hardware with the latest operating system. However, Exchange Server 2019 CU15 cannot be installed in environments that still have Exchange 2013 servers; all Exchange 2013 servers must be decommissioned and uninstalled before CU15 can be installed. (support.microsoft.com)

Conclusion

The release of CU15 for Exchange Server 2019 marks a pivotal moment in Microsoft's Exchange Server lifecycle. While the delay in its release posed challenges, it also provided organizations with additional time to plan their migration strategies. With the end-of-life date for Exchange Server 2019 approaching, it is imperative for organizations to act promptly to ensure a seamless transition to supported platforms, thereby maintaining security, compliance, and operational efficiency.