October 2025 is going to be a big month for saying goodbye to several aging Microsoft technologies. Not only is it the end of support for Windows 10, but it’s also the end of support for Exchange 2016 and Exchange 2019.

While there will be options going forward, the demise of these products comes with security concerns and quite frankly costs to consider. Microsoft has stated that, unlike it did Windows 10, it will not release any extended support updates for either Exchange 2016 or 2019

Those who wish to stay with an on-premises solution can consider Microsoft’s offering called Exchange Server Subscription Edition, or Exchange Server SE for short. The first release of this platform will be around the same time as the demise of Exchange 2016 and 2019.

Microsoft has stated that the migration pain will be minimal as the SE version will use the same code as Exchange Server 2019 CU15 with a few cosmetic differences. For example, the license agreement will be updated to reflect the name change and the build and version number will be updated.

Multiple versions of Exchange will not be allowed

Users will be able to perform an in-place upgrade on top of your existing infrastructure as well as a more legacy style migration, a lengthier process by which a new server infrastructure is created and mailboxes are moved to the new server.  During this process there is some disruption as the mailboxes can be temporarily paused or impacted by the migration process, but it typically can be planned around and minimized.

The Subscription Edition is exactly what it sounds like: users will be required to have subscription licenses or licenses with active software assurance for users and servers, with the addition of support for Server 2025. Exchange Server 2019 CU15 adds support for Transport Layer Security (TLS) 1.3 and reintroduces certificate management in the Exchange admin center.

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Source : https://www.csoonline.com/article/3823124/what-security-teams-need-to-know-about-the-coming-demise-of-old-microsoft-servers.html