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Microsoft Rolls Out Final Cumulative Update for Exchange Server 2019

Microsoft on Monday released the last cumulative update for Exchange Server 2019, marking the final major refresh before the product reaches its end of support on Oct. 14, 2025.

This  final update (2025 H1 Cumulative Update (CU15) introduces  new features, security enhancements and compatibility updates, while also providing hooks for Microsoft's upcoming Exchange Server Subscription Edition (SE).

One highlight of this final CU is the introduction of Feature Flighting, a cloud-based service for Exchange Server Subscription Edition (SE) that enables admins to test and roll out select new features without requiring a dedicated test environment. It leverages Office Config Service (OCS)for update management and allows Microsoft to disable problematic features if needed. 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.

As this will be the final official update, getting Exchange Server 2019 as secure as possible before loss of support is key. While Microsoft will continue to release security updates in its monthly security release and through out-of-band patches until January, it has also released a handful of updates aimed at strengthening Exchange Server 2019, including:

  • Partial TLS 1.3 Support: CU15 introduces TLS 1.3 for all supported protocols except SMTP on Windows Server 2022 and later.
  • Advanced Malware Scanning Interface (AMSI) Enhancements.
  • Extended Protection Enabled by Default: As a security best practice, Extended Protection remains enabled by default.

One feature not making it for this final release is support for Exchange Server SE product keys, which the company had previously said was going to be included with 2025 H1 CU. "We are delaying this change until Exchange Server SE CU1 to make sure that in-place upgrades from Exchange 2019 to Exchange Server SE RTM are as smooth and simple as possible," wrote Microsoft in a blog post. "Consequently, Exchange Server SE RTM will accept and honor Exchange 2019 product keys, and you won't need to update your servers to use an Exchange Server SE product key until Exchange Server SE CU1."

Microsoft has confirmed that when Exchange Serve SE drops later this year, it will be code-equivalent to Exchange Server 2019 CU15. The company said that those migrating from the latest version should only need to install a straightforward upgrade once SE is available. For those still on Exchange Server 2016, Microsoft recommends upgrading to Exchange Server 2019 CU15 now to be ready for SE.

Until the end of support and the introduction of Exchange Server SE, Microsoft said it will continue to work on a list of customer-reporting bugs it received, which will be delivered in future Hotfix Updates.

About the Author

Chris Paoli (@ChrisPaoli5) is the associate editor for Converge360.

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