Exchange Server CU15: Ready for Action! (2025 H1 + WS2025)
The Cumulative Update 15 (CU15, 2025 H1) for Exchange Server 2019 is now available. This is the final CU for Exchange Server 2019 and brings several enhancements and fixes for known issues. CU15 also includes support for Windows Server 2025, allowing organizations to deploy Exchange Server 2019 on the latest server platform.
- Ready for Action by IT-Admin to prepare sustainable for Exchange Server SE3 !
Exchange Server CU15 (2025 H1)
Support for Windows Server 2025
CU15 includes support for Windows Server 2025. Organizations can now install Exchange Server 2019 CU14 or CU15 on new servers and later perform an in-place upgrade to Exchange Server SE3. This ensures maximum lifecycle support for Exchange Server deployments.
Partial TLS 1.3 support, Feature Flighting, DocParser
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TLS 1.3 Support: CU15 introduces partial support for TLS 1.3 on Windows Server 2022 and later, covering all protocols except SMTP. Future updates will add SMTP support.
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Feature Flighting: This new server-side capability allows administrators to test and deploy select new features in Exchange Server SE. It uses Office Config Service (OCS) for updates and provides more control in rolling out changes.
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DocParser Integration: CU15 replaces previous parsing technology with Microsoft's DocParser for text extraction in transport processing, enhancing security and performance in Exchange Transport Rules and Data Loss Prevention.
Relaunch of Certificate management UI
CU15 restores certificate management tasks within the Exchange Admin Center (EAC). Previously removed functions, such as the ability to create, renew, and remove certificates, have now been restored.
- Import or export the exchange certificates (without PowerShell)
Download, Install and Validate Health
Administrators should follow these steps:
- Reboot Exchange Servers before installation to complete pending Windows Server updates.
- Download and Install 'Exchange Server 2019 Cumulative Update 15' (KB5042461)
- Run 'Exchange Server Health Checker' (https://aka.ms/ExchangeHealthChecker) after installation to verify system health.
Prepare for Exchange Server SE (2025 H2)
Opt-in for Windows Server 2025
Your Windows Server does have a lifetime by adopting Windows Server 2025, you can reduce future upgrade requirements.
Cloud Upgrade Path
Decide now whether to pay for the upcoming Exchange Server SE3 or move to Exchange Online with all your services or
explore third-party solutions for legacy SMTP applications (SMTP Relay).
- Upgrade to Exchange Online with or without High volume email (HVE) service
On-Prem Upgrade Path
- Upgrade to CU15 to prepare for Exchange Server SE expected 2025 H2/Q3
- Choose between a Legacy Upgrade or an In-Place Upgrade
- TLS 1.3 support is available starting from Windows Server 2022
| Steps | Description | Type | Exchange Server | Windows Server | Exchange Deprecation |
|---|---|---|---|---|---|
| 1 | Migrate to new windows server | Legacy Upgrade (Move) | 2016 | 2016, 2019, 2022 | Yes (EOS1: October, 2025) |
| 2 | Migrate to new windows server and newest CU2 | Legacy Upgrade (Move) | 2019 | 2016, 2019, 2022 | Yes (EOS1: October, 2025) |
| 3 | Install new release of CU152 | In-place Upgrade | 2019 | 2025, 2022 | Not yet |
| 4 | Install upcoming release of SE3 | In-place Upgrade | 2025 | SE | No |
Path from Exchange Server 2019
Path from Exchange Server 2016
Summary
I'm relieved that CU15 has finally been released, this gives us the opportunity to build on a structure which can stay for years to come. Now, the focus shifts to ensuring that all core software supports Windows Server 2025, so your datacenter is ready!
Wish you all a good day!
References:
- Released: 2025 H1 Cumulative Update for Exchange Server
- When is Exchange 2019 CU15 coming (and more news)
- T-9 months: Exchange Server 2016 and Exchange Server 2019 End of Support
- End of Support for Exchange Server 2016 and Exchange Server 2019: T-12 Months
- Upgrading your organization from current versions to Exchange Server SE
- Exchange Server Roadmap Update (2024.05)
- Exchange Server Roadmap Update (2022.06)
- Exchange News and Announcements – Microsoft Ignite 2020 Edition
- End of Support: Know your options (PDF)
- Lifecycle FAQ - Modern Policy