Microsoft has yet to deliver its promised Cumulative Update 15 for Exchange Server 2019 due to some issues, as the countdown to the end of support for the email platform continues.

Redmond told the world just before Christmas that December was not a good time to release a Cumulative Update (CU). Therefore, it was [1]pushing the release of the final CU for Exchange Server 2019 back into January 2025.

However, January has come and gone, and Redmond still hasn't delivered the anticipated update.

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Microsoft customers will be used to delays, but this one is slightly more concerning than others, since Exchange Server 2019 itself is due to run out of support on October 14, and the update is needed to help organizations with the transition.

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The successor to Exchange Server 2019, Exchange Server SE, is still expected to be released early in the third quarter of this year. Microsoft has indicated that CU15 will enable customers to upgrade an existing Exchange Server 2019 deployment to a build that is code-equivalent to the initial release of Exchange Server SE, excluding interim updates, branding changes, and licensing differences.

In a post on the software giant's [5]Exchange Team Blog on January 31, it gave some hints about the reasons for the delay, but provided no indication as to when the update might be expected.

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"We have committed to Exchange Server CU15 being the 'code equivalent' to Exchange Subscription Edition (SE) RTM release (other than updates released in interim, as well as changed branding and EULA). Therefore, CU15 is the last chance that we have if we want to release any Exchange features before Exchange SE CU1. CU15 does include new features which added complexity to this release," Microsoft says.

[7]Exchange update refusenik? Consider yourself warned by Microsoft

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[9]Microsoft delays final Exchange Server 2019 Cumulative Update to 2025

[10]Microsoft patches the patch that broke Exchange Server

According to the blog, customers enrolled in Microsoft's Technology Adoption Program (TAP) have reported some issues with CU15, so the team decided to address them and create a new CU15 build. This has effectively meant a reset of the testing process, hence the delay in the public release.

We asked Microsoft to provide a target release date for its updated CU15 build, but haven't heard back.

The good news is that this should mean CU15 is being tested more thoroughly than the [11]November 2024 Security Update (SU) , which broke transport rules and disrupted the flow of email for some users.

But it also means that companies will have even less time to perform an update before the end of support for Exchange Server 2019, as the blog states: "We are not changing any of our already announced lifecycle dates."

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And for anyone still on an earlier release of the email server platform, Microsoft's advice is to upgrade to Exchange Server 2019, install the latest update, and upgrade in place to Exchange Server SE once that becomes available. ®

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[1] https://www.theregister.com/2024/12/10/microsoft_exchange_server_cu/

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[5] https://techcommunity.microsoft.com/blog/exchange/when-is-exchange-2019-cu15-coming-and-more-news/4372765

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[7] https://www.theregister.com/2025/01/24/microsoft_has_a_warning_for/

[8] https://www.theregister.com/2025/01/09/microsoft_enterprise_impacting_retirements/

[9] https://www.theregister.com/2024/12/10/microsoft_exchange_server_cu/

[10] https://www.theregister.com/2024/11/28/microsoft_fixes_broken_exchange_server/

[11] https://www.theregister.com/2024/11/28/microsoft_fixes_broken_exchange_server/

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[13] https://whitepapers.theregister.com/