Today Microsoft released CU15 for Exchange Server 2019. CU15 is an important update for Exchange Server 2019: Firstly, it is the last CU to be released for Exchange 2019 and secondly, it brings Exchange 2019 onto the same code base as Exchange Server SE.
After installing Exchange Server 2019 CU15, an inplace upgrade of the Exchange Server (not the operating system) to Exchange Server SE (to the RTM version) can be performed. During the inplace upgrade from CU15 to Exchange Server SE, only the version number and the license will be changed. There will be no new features with Exchange RTM. New features are only included in CU15 and later in CU1 for Exchange SE.
Click here to download Exchange Server 2019 CU15:
Here is an overview of the new functions that are available with Exchange 2019 CU15:
Exchange Server Feature Flighting
Feature Flighting offers administrators an additional way to test and introduce selected new features in their Exchange Server SE organization. Feature Flighting is an optional cloud-based service for on-premises Exchange Servers. It uses the Office Config Service (OCS), the same endpoint used by the Emergency Mitigation Service and Microsoft Office clients, to check for updates from Microsoft related to released features.
Feature Flighting allows administrators to deploy updates immediately and control when a feature is activated in their environment. Feature Flighting also allows Microsoft to disable a feature if a serious problem is discovered after the update has been released.
However, feature flighting will only become relevant with Exchange Server SE, as there are and will be no corresponding features in CU15.
Optional diagnostic data
From CU15, Exchange Server collects Additional diagnostic data and sends it to Microsoft, including additional information about disabled functions. This additional data is only collected and sent if diagnostic data is enabled on the server.
Support for Windows Server 2025
Exchange Server 2019 CU15 provides support for Windows Server 2025 (support has also been added for CU14 subsequently submitted). Support for the Active Directory on Windows Server 2025 is now also new for both CUs. This means that Exchange Server 2019 CU14 and CU15 support Windows Server 2025 for the installation of the Exchange Server, as well as domain controllers with Windows Server 2025.
DocParser replaces Oracle Outside In technology
As of CU15, Exchange Server uses DocParser as a replacement for the Oracle Outside In technology previously used in Exchange Server. DocParser is a Microsoft library that was developed to parse various file formats. It performs text extraction when processing emails in transport for Data Loss Prevention and Exchange Transport Rules.
Partial TLS 1.3 support
As of CU15, Exchange 2019 supports TLS 1.3 on Windows Server 2022 and higher for all protocols except SMTP. If CU15 is installed on Windows Server 2022 or higher, TLS 1.3 is enabled by default.
Support for TLS 1.3 for SMTP will be added in a future update.
Improvements to the Exchange Server AMSI integration
The improved Exchange Server AMSI integration (previously available in the November 2024 SUs announced) is also included in CU15.
The user interface for certificate management is available again in the EAC
Some important certificate management tasks were removed from the EAC in an earlier CU. With CU15, certificate management will be included in the EAC again.
Coexistence with Exchange Server 2013 is blocked
Exchange Server 2019 CU15 cannot be installed in an organization running Exchange 2013 servers. All Exchange 2013 servers in the organization must be decommissioned and uninstalled before Exchange 2019 CU15 can be installed.
Upgrade path from Exchange Server 2019 to Exchange Server SE RTM
The upgrade from Exchange 2019 (and also Exchange 2016) is described in detail in a separate article. Essentially, however, the classic migration and now also the Inplace Upgrade are available. However, the Inplace Upgrade only refers to the Exchange Server, not the operating system.
