Exchange Server Subscription Edition: An IT Pro Guide to Exchange Server in 2025
Exchange Server Subscription Edition CU1 will be the only supported version of Exchange Server
Last Update: Apr 04, 2025 | Published: Apr 02, 2025
Exchange Server Subscription Edition (ESSE) is the new version of Microsoft’s on-premises email and calendaring solution, due to be released early Q3 of 2025. This blog post provides a detailed overview of Exchange Server Subscription Edition, tailored for IT professionals new to Exchange Server or transitioning from older versions.
Discover how little is new with ESSE (beyond branding) – learn about licensing models, deployment prerequisites and considerations, and how it’s different from Exchange Server 2016/2019. Whether planning a migration/upgrade or starting fresh, this guide will assist you with the knowledge for a smooth rollout.
What is Exchange Server Subscription Edition?
Microsoft (on-premises) Exchange Server has joined the subscription model bandwagon. The days of Exchange Server 2013, 2016, and 2019 are ending. Functionally, the general release of Exchange Server Subscription Edition (RTM) will be identical to the just-released Exchange Server 2019 CU15 (Cumulative Update 15). The only code changing is the display name and marketing name of the product, from Exchange Server 2019 to Exchange Server Subscription Edition.
💡Exchange Server Subscription Edition is not the same as Exchange Online, Microsoft’s cloud-based service/version of Exchange Server.
Key differences from Exchange Server 2016/2019
Honestly, besides naming conventions throughout the product and the deployment bits themselves, no new features are being introduced in the initial release of Exchange Server Subscription Edition (ESSE). For existing installations of Exchange Server 2019, when you upgrade from CU15 to ESSE, nothing will change.
So, what is changing? Well, there are some important fundamental changes before/when implementing ESSE.
- As is the case with Exchange Server Cumulative Update 15 (CU15), you’ll need to retire or upgrade all Exchange Server 2013 servers. Setup will halt if you have 2013 servers around.
- Support for new product keys will also be included. You will need to obtain new product keys to install and activate ESSE. These new volume license keys will be available on the M365 admin center website along with the installation media (ISO).
- And finally, support for Windows Server 2025 is included. Today, Exchange 2019 CU14/15 can be installed on Windows Server 2019, Windows Server 2022, and Windows Server 2025. CU14 introduced support for Windows Server 2025.
Licensing and subscription model
The licensing for Exchange Server is changing with this latest release. The installation media will be available for download from the Microsoft 365 admin center website (formerly the Microsoft Volume License Service Center website) in the early part of Q3 of 2025.
The licensing model will be similar to SharePoint Server Subscription Edition. Microsoft is no longer offering purchases of licenses only. In addition to the required Server licenses and CALs, customers will need an active subscription.
This means purchasing either cloud subscription licenses for all covered users and devices, or Exchange Server SE server licenses and CALs with Software Assurance.
Is there anything new in Exchange Server Subscription Edition?
First of all, the hardware and operating system requirements for Exchange Server SE will be identical to Exchange 2019 CU15. Windows Server 2025 support was added with Exchange Server 2019 CU14.
Importantly, there will be no changes to the schema for Active Directory when upgrading from Exchange Server 2019. The Windows Server 2012 R2 forest functional level will continue to be supported.
Finally, as I stated above, there are no functional changes in Exchange Server SE from Exchange Server 2019 (CU15).
Okay, let me be pedantic for just a moment and list the actual changes when deploying the RTM version of ESSE.
- The License agreement, an RTF file shown only in the GUI version of Setup, will be updated.
- The name will change from Microsoft Exchange Server 2019 to Microsoft Exchange Server Subscription Edition.
- The build and version number will be updated.
Yes, that’s it.
Deployment scenarios and options
There are two high-level deployment scenarios for Exchange Server SE. To help further accelerate in-place upgrades, in addition to being code equivalent, Exchange Server SE will support two types of upgrades:
- in-place
- and legacy
In-place upgrades (from Exchange Server 2019)
The fastest and easiest method to go from Exchange Server 2019 to Exchange Server SE is to run an in-place upgrade. Thankfully, the upgrade experience will be equivalent to a Cumulative Update (CU). After you’ve upgraded to ESSE, it will be updated twice a year with the latest CUs.
Legacy upgrades
The more time consuming effort is performing a legacy upgrade of Exchange Server. This involves building out a new infrastructure and moving namespaces and mailboxes to the new location. If your organization is running Exchange Server 2016, you’ll have one more legacy upgrade to take part in and plan for.
The recommended option from Microsoft is to plan and perform a legacy upgrade now to Exchange Server 2019 CU15. You’ll then be able to perform the easy in-place upgrade to Exchange Server SE.
Yes, this is somewhat complicated. Here’s a table from Microsoft to assist your planning.
| Version in use | Exchange 2019 CU15 | Exchange Server Subscription Edition (SE) |
| Exchange Server 2013 | Not supported in the organization. No coexistence supported. Legacy upgrade to Exchange 2019 CU14 now, remove Exchange 2013, and update to Exchange 2019 CU15. | Not supported in the organization. No coexistense supported. Legacy upgrade to Exchange 2019 CU14 now. Remove Exchange 2013, update to CU15 and in-place upgrade to Exchange Server SE when available. |
| Exchange Server 2016 CU23 | Legacy upgrade to Exchange 2019 CU15 now. | Legacy upgrade to Exchange 2019 CU15 now, and in-place upgrade to Exchange Server SE when available. |
| Exchange Server 2016 CU22 and earlier | Not supported in the organization. Legacy upgrade to Exchange 2019 CU15 now ; or update to Exchange 2016 CU23 now, and then legacy upgrade to Exchange 2019 CU15. | Not supported in the organization. Update to Exchange 2016 CU23 and legacy upgrade to Exchange 2019 CU15, then in-place upgrade to Exchange Server SE when available. |
| Exchange Server 2019 CU14 / CU15 | Update CU14 servers to Exchange 2019 CU15 if you want to try Exchange SE RTM “equivalent” in your organization. | In-place upgrade to Exchange Server SE. |
| Exchange Server 2019 CU13 | This version is out of support with Exchange 2019 CU15 release. Update to Exchange 2019 CU15. | This version will be out of support when Exchange SE is released. Update to Exchange Server 2019 CU15, and then in-place upgrade to Exchange Server SE. |
| Exchange Server 2019 CU12 and earlier | Not supported in the organization. Update to Exchange 2019 CU15 now. | Not supported in the organization. Update to Exchange Server 2019 CU15, then in-place upgrade to Exchange Server SE. |
Important Exchange Server support dates
It is important to keep updated on the support end dates, or end of life, for various versions of Exchange Server. Remember – unsupported versions will no longer receive security patches or updates.
| Exchange Version (Build) | End of Support | Support status at the time of release of… | ||
| Exchange 2019 CU15 | Exchange SE RTM | Exchange SE CU1 | ||
| Exchange 2013 (any CU) | April 11, 2023 | Not Supported | Not Supported | Not Supported |
| Exchange 2016 CU23 | October 14, 2025 | Extended Support | Extended Support | Not Supported |
| Exchange 2019 CU14/CU15 | October 14, 2025 | Extended Support | Extended Support | Not Supported |
Exchange Server SE Cumulative Update 1 (CU1)
If you want to plan your on-premises Exchange Server strategy throughout the rest of 2025, you’ll want to know more about Exchange Server SE Cumulative Update 1 (CU1). Microsoft is planning to release CU1 for Exchange Server Subscription Edition in October of 2025, as part of the 2025 H2 release (2nd half of 2025).
Planned features for Exchange Server SE
Here are the planned enhancements for Exchange Server SE CU1:
- Kerberos for server-to-server communication
- Adding support for an Admin API and deprecating RPS
- Removing Outlook Anywhere (!)
- Removal of support for co-existence with earlier versions
- Updating the Visual C++ redistributable to the version that ships with Visual Studio 2022
- Removal of support for UCMA 4.0 and the instant messaging feature in Outlook on the web
This is VERY important – at the time of the CU1 release, Exchange Server Subscription Edition will be the ONLY supported version of Exchange Server!
Yes, read that again. I’ll wait. During the Exchange Server Setup program for CU1, it will block coexistence with anything other than Exchange Server SE RTM or later.
This is a lot to absorb and ingest. Feel free to leave a comment or question below – thank you for reading.