Why Organisations Still Running On-Premises Exchange Need to Act Now: Exchange Server Subscription Edition Explained

If your organisation is still running Exchange Server 2016 or 2019 on-premises, you’ve likely heard the term “Exchange Server Subscription Edition” floating around. But with so much noise in the Microsoft ecosystem, it can be hard to separate what actually matters from what’s just marketing.

This article cuts through that. Here’s what Exchange Server SE is, why the end-of-support deadline is a genuine risk, and what your upgrade path looks like.

What Is Exchange Server Subscription Edition?

Exchange Server Subscription Edition (officially released by Microsoft in July 2025) is the latest and reportedly final version of on-premises Exchange Server. It represents a significant shift in how Microsoft licenses and delivers Exchange: rather than the traditional perpetual licence model (buy once, use for several years), Exchange SE moves to a subscription-based model, similar to what Microsoft already uses for SharePoint Server Subscription Edition and, of course, Microsoft 365.

From a technical standpoint, Exchange SE at release is built directly on Exchange Server 2019 CU15. Under the hood it is largely the same product. The more meaningful changes are in licensing, lifecycle, and the path forward.

The real news is what comes with Exchange SE going forward: continuous updates, security patches, and feature improvements delivered on an ongoing basis rather than in large infrequent cumulative updates. Think of it as Exchange moving to a “Windows as a Service” model.

The End-of-Support Deadline Is Real, and It Has Passed

Microsoft ended support for both Exchange Server 2016 and Exchange Server 2019 on October 14, 2025. This is not a soft deadline. Microsoft has been explicit that there will be no extension of the end-of-life date, and no Extended Security Updates (ESU) were planned, though a limited ESU contingency programme was subsequently announced for organisations that genuinely could not complete migration in time.

What does end of support mean in practice?

• •No more security patches. Any vulnerabilities discovered after October 14, 2025 will not be addressed by Microsoft for Exchange 2016 or 2019. Given Exchange’s history as a high-value attack target (including the significant vulnerabilities exploited in recent years) this is a material security risk, not a theoretical one.
• •No technical support. If something breaks, Microsoft will not assist. For organisations running business-critical email infrastructure, this raises serious operational risk.
• •Compliance exposure. For organisations in regulated industries (finance, healthcare, education, legal) running unsupported, unpatched email infrastructure can create real compliance and audit issues. Regulatory frameworks increasingly require vendors and service providers to run supported, patched software.

If your Exchange environment is still on 2016 or 2019 with no upgrade plan, this is the most important reason to act.

Why Not Just Move to Exchange Online?

It’s a fair question. Microsoft 365 and Exchange Online are excellent for many organisations, and for those without specific reasons to stay on-premises, the cloud-first path often makes sense.

But not every organisation can or should move to Exchange Online. Common reasons include:

• •Data sovereignty requirements: some industries or government-adjacent organisations have obligations around where email data is stored and processed
• •Compliance and regulatory constraints: certain regulated industries require on-premises control over email archiving, DLP, and audit trails
• •Hybrid complexity: large organisations with complex Active Directory environments, third-party integrations, or custom mail flow configurations may find a full Exchange Online migration costly and disruptive
• •Latency or connectivity considerations: some environments simply perform better with local mail infrastructure

For these organisations, Exchange Server SE is not a compromise. It’s the right answer.

What’s the Upgrade Path to Exchange SE?

This is where Microsoft has actually made things easier than previous Exchange upgrades.

If you’re running Exchange Server 2019 CU14 or CU15, you can perform an in-place upgrade to Exchange SE. This is a significant improvement over historical Exchange migrations, which typically required building a parallel environment, migrating mailboxes, and decommissioning the old infrastructure. The in-place path means your configuration, mailbox data, and customisations can be retained with far less disruption.

If you’re running Exchange Server 2016, you cannot upgrade in-place to Exchange SE directly. You’ll need to introduce Exchange SE into the environment alongside your existing 2016 servers, migrate mailboxes, then decommission 2016. Note that Exchange SE CU1 (scheduled for the first half of 2026) and the current SE RTM both support coexistence with Exchange 2016 and 2019, but Exchange SE CU2 (planned for the second half of 2026) will block coexistence with all previous versions. That gives you a window, but it’s not unlimited.

Licensing: What Changes?

Exchange SE requires subscription licences, either a new subscription or existing licences with active Software Assurance. This is the same model as SharePoint Server Subscription Edition. If your organisation’s Software Assurance has lapsed or you’ve been running on perpetual licences without SA, you’ll need to factor licence costs into your upgrade planning.

Microsoft has confirmed a free Hybrid server licence will continue to be available for organisations running Exchange in hybrid configurations with Microsoft 365.

What Should You Do Now?

If you’re still on Exchange 2016 or 2019, here’s a practical action plan:

• •Assess your current state. What version are you on? What CU level? What’s your mailbox count and data volume? Do you have any third-party connectors or applications that depend on Exchange?
• •Decide: Exchange SE or Exchange Online? This decision depends on your compliance requirements, data sovereignty obligations, hybrid complexity, and budget. Both are valid paths, the wrong answer is doing nothing.
• •Check your licensing position. Do you have active Software Assurance? When does it expire? Talk to your Microsoft licensing partner to understand your position before starting.
• •Plan your upgrade window. If you’re on Exchange 2019 CU14 or CU15, an in-place upgrade to Exchange SE is the fastest path. If you’re on Exchange 2016, you need a migration plan that accounts for the CU2 coexistence deadline in the second half of 2026.
• •Get help if you need it. Exchange upgrades (even in-place ones) involve real risk if not planned carefully. DNS, certificates, mail flow, connector configuration, and hybrid settings all need to be validated.