Exchange Server Subscription Edition (SE) is now the only supported on-premises version of Exchange. Technically it started life as Exchange 2019 CU15 with a new name, but the lifecycle, licensing and servicing rules around it are different, and those are what trip up upgrade projects. In this post I'll explain how SE works, what you need to license it, and give you a planning checklist to get every server onto it.
Status (October 2026): Exchange Server SE RTM shipped on 1 July 2025 (build 15.2.2562.17) and is still the only SE baseline. Cumulative Update 1 has not been released: in August 2026 the Exchange team said it has no release date yet because security fixes are taking priority. The newest build is SE RTM Sep26SUv2 (15.2.2562.53, released 2 October 2026). Re-check Microsoft's build numbers page before you plan, because it changes almost every month.
How Exchange Server SE works: lifecycle and servicing#
Earlier versions had a fixed lifecycle and a hard end date. SE follows Microsoft's Modern Lifecycle Policy instead: there is no end-of-support date as long as you stay current, and there will be no more year-numbered versions. The codebase is serviced continuously. Microsoft has also committed to continued support for Exchange Server, SharePoint Server and Skype for Business Server through at least 2035.
"Staying current" is the price of that model. Updates arrive in three forms:
- Cumulative Updates (CUs) – full builds of the product. Microsoft's stated cadence is two per calendar year, and a CU can change prerequisites, add features or remove them.
- Security Updates (SUs) – security fixes for a specific CU. Since mid-2026 they have shipped monthly.
- Hotfix Updates (HUs) – non-security fixes and occasionally new functionality, also tied to a specific CU.
Plan Exchange like any evergreen product: a monthly window for SUs and HUs, and a twice-yearly project slot for CUs.
Licensing: what you need to run SE#
SE uses an entitlement model: you need an active qualifying entitlement to install it, run it and keep receiving updates. According to Microsoft's Exchange licensing FAQ, that entitlement comes from either:
- Exchange Server Standard or Enterprise server licences with active Software Assurance (SA), or
- a qualifying Microsoft 365 subscription (for example Microsoft 365 E3 or E5) that includes on-premises server use rights (Extended Use Rights).
On top of that, every user or device that accesses SE needs a Standard CAL, plus an Enterprise CAL for the advanced compliance features. CALs must also be covered by SA or an equivalent subscription; Exchange Online Plan 1 and Plan 2 give CAL equivalency. Details that matter in practice:
- You need one server licence per running instance, physical or virtual. Standard Edition mounts up to five databases; Enterprise up to 100.
- Extended Use Rights only cover licensed users – one E5 licence doesn't license a whole on-premises organisation.
- Outlook is licensed separately. The FAQ states that the Outlook client licence is no longer included with any Exchange CAL and must be bought separately for SE. The SE Standard CAL covers mail, calendar, contacts and tasks through Outlook on the web or on mobile devices over Exchange ActiveSync, so confirm how every Outlook client that connects to SE is licensed.
- A hybrid server that hosts no mailboxes and is used only for recipient management can be licensed with the hybrid key the Hybrid Configuration Wizard provides. Servers that host mailboxes, run Edge Transport or relay SMTP need a full licence.
- If your Exchange 2019 licences have no active SA, you need a new entitlement. Confirm your position with your licensing partner early.
Product keys: SE RTM doesn't need a new key, and servers keep working after an in-place or legacy upgrade. Microsoft has said a future CU will introduce an SE-specific key requirement, so read the release notes of every CU.
What changed compared with Exchange 2019#
SE RTM is code-equivalent to Exchange 2019 CU15: only the licence agreement, product name and build number differ, there were no Active Directory schema changes, and prerequisites and supported operating systems (Windows Server 2019, 2022 and 2025) are the same. The differences are around it:
| Area | Exchange 2019 | Exchange Server SE |
|---|---|---|
| Lifecycle | Fixed; ended 14 October 2025 | Modern Lifecycle, no end date while current |
| Licensing | Perpetual licence plus CALs | Active SA or qualifying subscription required |
| Updates | ESU customers only, ending with October 2026 | Public SUs, HUs and CUs |
| Coexistence | CU15 blocks Exchange 2013 | RTM blocks 2013; CU2 will block 2016 and 2019 |
| Hybrid rich coexistence | EWS only; stops when EWS is disabled in Exchange Online (April 2027) | Microsoft Graph-based free/busy and photos from the May 2026 HU |
OWA Light has also been disabled, starting with the August 2026 security update.
Upgrade planning, step by step#
1. Inventory every Exchange server#
Get-ExchangeServer | Format-Table Name, ServerRole, Edition, AdminDisplayVersion -AutoSizeAdminDisplayVersion shows the CU only. Run the Health Checker on every server to see the SU level and configuration problems – see my Health Checker guide.
2. Remove Exchange 2013#
SE setup refuses to install while any Exchange 2013 server exists in the organisation.
3. Pick a path for each server#
- Exchange 2019 CU14 or CU15: in-place upgrade, just like installing a CU – see the in-place upgrade walkthrough.
- Exchange 2016: legacy upgrade – install new SE servers, move mailboxes and services, then decommission.
- New hardware or a newer Windows Server: also a legacy upgrade, because in-place OS upgrades with Exchange installed aren't supported.
4. Check prerequisites and dependencies#
Confirm .NET Framework (4.8.1 is recommended on Windows Server 2022 and 2025; Windows Server 2019 uses 4.8), the Visual C++ 2012 and 2013 runtimes and the IIS URL Rewrite module. Ask your backup, antivirus, load balancer and archiving vendors to confirm SE support.
5. Plan the hybrid changes#
With mailboxes still on-premises, hybrid rich coexistence needs the dedicated Exchange hybrid app, and the move to Microsoft Graph needs SE with the May 2026 HU or later. My hybrid free/busy article covers the app and how to test it.
6. Set a deadline for coexistence#
Exchange 2016 and 2019 can coexist with SE only until SE CU2, which won't install while they are present. Make "no 2016 or 2019 servers left" a milestone well before then.
Verify where you stand#
Get-ExchangeServer | Format-List Name, Edition, AdminDisplayVersion
Get-Command ExSetup.exe | ForEach-Object { $_.FileVersionInfo }Good looks like: every server reports Version 15.2 (Build 2562.17) in AdminDisplayVersion, ExSetup.exe on each server shows 15.02.2562.053 or later, and the Health Checker shows no red findings.
Tips and gotchas#
- Don't wait for CU1. Microsoft's guidance is to upgrade to SE as soon as possible and keep it current; CU1 will install like any other CU when it arrives.
- Install SUs on workstations that run the Exchange Management Tools too, so tools and servers stay compatible.
- Keep DAG members on the same build and patch them one at a time – see DAG maintenance mode.
- Build the licensing case, Outlook client licences included, before the technical work, so procurement doesn't hold up the cut-over.
