Exchange Server Subscription Edition (SE) was released on July 1st, and in the tenants I work with, the pressure to modernise on-premises Exchange has suddenly become very real. Support for Exchange Server 2016 and 2019 ends on October 14, 2025, so admins have some hard decisions ahead and not much time to make them. In many organisations the Exchange servers have turned into a maintenance burden. Letting them fall out of support still isn't an option, especially after the recent security incidents and with Microsoft moving to subscription models faster and faster.

Subscription Edition matches Exchange 2019 CU15 but changes the licensing

With the Subscription Edition, Microsoft brings the cloud release cadence to on-premises Exchange. At release, the code is equivalent to Exchange 2019 CU15. For most environments that keeps the upgrade path pleasantly simple. If your servers run Exchange 2019 CU14 or CU15, you can upgrade in place to SE, with no parallel installation and no rebuilding the configuration from scratch. Anyone on an older CU has to get to CU14 or CU15 first.

The real change is the licensing. Exchange Server SE is only available as a subscription (or with active Software Assurance). Perpetual licences are gone. Not every customer will be happy about that, but it is now the only way to keep getting support, security updates and future improvements. Microsoft also applies its modern lifecycle policy to SE, so updates will come more often and the years-long gaps between releases are over. Supported configurations are much the same as for Exchange 2019 CU15, and the current state is always listed in the official requirements.

Support for Exchange 2016 and 2019 really does end in October

The October 14, 2025 date won't move. After that there are no new security fixes and no support. In many hybrid environments I still hear that a "management-only" Exchange server can simply keep running. It can't. Microsoft has been clear that unsupported servers are a risk, and hybrid environments in particular rely on a supported Exchange for recipient management. I've written in more detail about the end of support and its effect on hybrid setups in an earlier post.

Practical tip: If you run hybrid and have no mailboxes left on-premises, take a look at the Exchange Management Tools Only install. It is the officially supported way to manage synced attributes without running a full Exchange server.

The in-place upgrade starts from Exchange 2019 CU14 or CU15

An in-place upgrade to Exchange Server Subscription Edition requires Exchange 2019 CU14 or CU15. Nothing older will work. If you're still on 2016 or an old 2019 build, the first job is to get current. Platform requirements have barely changed since CU15, but I'd still check the build numbers and release dates carefully before planning anything.

If you've done your homework, the process itself is simple. Start setup, choose Subscription Edition, enter your subscription key or proof of SA, and let it run. Databases and configuration stay in place, so downtime is short. I still never do this without a full backup. In larger or hybrid environments, a trial run in a lab tenant can spare you some unpleasant surprises.

The typical upgrade flow looks like this:

flowchart TD
    OldEX["Exchange 2019 CU14/CU15"] --> Upgrade["In-place upgrade SE"]
    Upgrade --> SE["Exchange Server SE"]
    SE --> Licence["Subscription/SA required"]
    SE --> Updates["Support & updates"]

Figure: Upgrade path to Exchange Server Subscription Edition.

Hybrid setups can often get by with the Management Tools Only

I see the same pattern in almost every project. Most organisations running hybrid Exchange moved all their mailboxes to the cloud long ago and keep the on-premises Exchange only for user management. So do they actually need a full Exchange Server, or would the Management Tools Only setup do? Microsoft built the latter for exactly this case. You get the UI and cmdlets for managing synced attributes, but no mailbox hosting and no transport roles.

The difference matters for operations and for the budget. If you only use the Management Tools and have no mailboxes on-premises, you don't need a Subscription Edition licence. If any mailboxes are left, or hybrid mail delivery is still in use, you have to deploy SE and keep a valid subscription.

I would plan the next few months like this

Exchange admins don't have much slack. If you're on Exchange Server 2016 or a 2019 build older than CU14, start preparing now:

  • Update to CU15 as soon as you can
  • Check your licensing: do you have subscriptions or active SA?
  • Decide whether you need full SE or can switch to Management Tools Only
  • Test the upgrade in a lab if your environment is complex
  • Finish the move to SE well ahead of the October 2025 deadline

With growing security threats, regulatory pressure and Microsoft's new support model, putting this off isn't really an option. For some of you, this could be the last major on-premises Exchange upgrade you ever do. Plan it properly and you'll sleep better next autumn.