What changes with Extended Support?

This means that from now on, Microsoft will not add any new features or non-security-related bug fixes for Exchange Server 2019. However, security updates and paid support on a limited basis will still be available until October 14th, 2025. Organizations have been given this period to plan and implement migration strategies to newer versions of Exchange Server.

Microsoft has announced that it will release two more Cumulative Updates (CUs) for Exchange Server 2019: CU14 and CU15. CU14 is in its final stage of testing and validation and is expected to be released soon. On the other hand, CU15 is scheduled to be released in 2024.

In software, Cumulative Updates (CUs) are packages that bundle together multiple smaller updates and releases. In the context of Exchange Server 2019, the upcoming CUs (CU14 and CU15) are particularly significant as they will be the last updates released for the software during its Extended support phase.

https://mspoweruser.com/microsoft-exchange-server-2019-enters-extended-support-from-mainstream-support/