The release of the 2025 H1 Cumulative Update (CU15) for Exchange Server 2019 is significant as it marks the final update for this server version. Delayed due to necessary security work, CU15 is critical for organizations transitioning to end-of-life support before October 2025. With CU13 out of support and exchange compatibility with 2013 severed, administrators must uninstall Exchange 2013 servers to install CU15. The update introduces Exchange Server Feature Flighting to streamline deployment without testing in a separate environment, aiming to mitigate previous delays in rolling out essential updates.
"Microsoft attributed the delay to 'necessary security work.' It said that since it could validate CU14 with Windows Server 2025, it would support CU14 and CU15 until the server reaches the end-of-life date."
"You must decommission and uninstall all Exchange 2013 servers from your organization before you can install CU15."
"The release means CU13 is out of support, and coexistence with Exchange Server 2013 has been blocked."
"This is an important task, but it is also time-consuming, and it can slow down the deployment of important updates. Moreover, not all organizations have test environments."
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