Exchange Server: An Even Tighter SE Squeeze

Mary Jo Foley is the Editor in Chief at Directions on Microsoft. Before joining Directions, Mary Jo has worked as... more

Microsoft has been planning to quick-march customers of its Exchange Server enterprise e-mail software to subscription licensing with the coming Exchange Server SE release. But a key piece in its plan is late, which means customers will have to march even quicker.

Central to Microsoft’s plan is Exchange Server SE (subscription edition), which Microsoft has said will be available early in the third quarter of this year. Exchange Server SE will be the first new on-premises release of Exchange since Exchange Server 2019. Like SharePoint Server SE and Skype for Business SE, the coming Exchange release will require a subscription (or Microsoft’s subscription-like Software Assurance) in order to receive updates and security fixes.

Very shortly after Microsoft releases Exchange Server SE, both Exchange Server 2016 and 2019 will no longer be supported by Microsoft. On Oct. 14, 2025, customers of Exchange Server 2016 and 2019 will have to either leave Exchange Server for a cloud replacement (such as Microsoft’s Exchange Online) or move to Exchange Server SE.

To help customers comply with its tight roadmap, Microsoft planned to release an update to Exchange Server 2019, Cumulative Update 15 (CU15), which officials said would transform that Exchange Server 2019 into a product virtually identical to Exchange Server SE.

Update (February 10): Microsoft announced that it is making CU15, also known as the H1 2025 Cumulative Update for Exchange Server 2019, generally available as of today, February 10, 2025. Back to the rest of our original blog post:

CU15: Still a No-Show

However, CU15 has gone missing. In May last year, Microsoft said to expect CU15 sometime in the second half of 2024. In Sept., Microsoft quietly updated its blog post about its Exchange Server rollout roadmap by changing the CU15 due date to “H1 2025.” But then in Dec. 2024, officials said CU15 was on track to release in early Jan. 2025.

Directions on Microsoft asked Microsoft last week for an update on CU15’s release. After telling us the company had no comment, Microsoft released on Jan. 31 a blog post with answers to the questions we asked.

In the post entitled “When is Exchange 2019 CU15 coming (and more news),” company officials said they are still not ready to publicly release CU15 due to some unspecified “late issues” discovered by customers in its Technology Adoption Program.

But “We are almost ready for the release,” officials stated. (We analysts are not holding our breath at this point.)

Officials reiterated that Microsoft is not going to push back the timing of the RTM version of Exchange Server SE, which is still due in early in the second half of calendar 2025. In spite of the ongoing CU15 delays, Microsoft also is not postponing the end of support for Exchange Server 2016 or 2019; both still will get no more updates or security patches after Oct. 14, 2025.

A New Wrinkle: CU14 Supports Windows Server 2025

The blog post also said that Microsoft has updated Exchange Server 2019 CU14 so that it can run on Windows Server 2025 “so customers can build new servers on new hardware and OS.” Support for Windows Server 2025 was one of the features Microsoft had promised for CU15.

Customers posted a number of questions about this new revelation in the comments section of the blog post. They asked whether they would be able to upgrade Exchange 2019 CU14 directly to Exchange SE. They wondered whether CU14 supported the Windows Server 2025 Domain/Forest Function Level. They asked if the prerequisites would remain the same for CU15/SE. Microsoft had not responded to any of these questions as of Feb. 3.

One Silver Lining

There is one silver lining to this delay: It suggests that Microsoft is treating CU15 like a full-blown product release and taking the time to test it thoroughly, said Directions on Microsoft analyst Rob Helm.

In the end, customers determined to keep their e-mail systems on-premises or in hosting at a third party have to upgrade to Exchange Server 2019 (if they are still running the 2016 version). They can then use the time waiting for CU15 to do data archiving or other clean-up projects that could make the upgrade to SE go more quickly. They can also line up the people, labs, and other resources to deploy CU15 as soon as possible after it arrives.

A reminder: Exchange Server SE CU1, due in late 2025, will kill support for coexistence with Exchange Server 2016 and 2019 servers, eliminate the 2010-era Outlook Anywhere protocol, and deliver other possibly disruptive changes. Directions asked Microsoft if there would be any exceptions for customers who might need to run older versions while migrating from 2016 or 2019 to SE. Microsoft officials did not provide an answer to that particular question in its blog post.