Microsoft has announced an optional 6-month Extended Security Update (ESU) program for Exchange Server 2016 and 2019, providing a temporary bridge for organizations struggling to complete their migrations before the upcoming end-of-support deadline. This program represents Microsoft’s response to customer feedback indicating that some organizations need additional time to finalize their transitions to Exchange Subscription Edition (SE).
Why This Program is Necessary
The ESU program addresses the imminent October 14, 2025 end-of-support date for both Exchange Server 2016 and 2019. After this date, Microsoft will no longer provide technical support, bug fixes, security patches, or time zone updates for these versions. Organizations continuing to run these unsupported versions face significant security vulnerabilities, compliance risks, and operational challenges.
With Exchange Server Subscription Edition (SE) now available since July 1, 2025, organizations have a clear migration path forward. However, the tight timeframe between the SE release and the October end-of-support date creates pressure for organizations to execute their migrations quickly and efficiently.
Target Audience for the ESU Program
Microsoft has designed this program for a very specific customer profile. The ESU is intended only for organizations that:
- Are unable to finalize their migrations to Exchange SE before October 14, 2025
- Already use Exchange 2016 CU23 or Exchange 2019 CU14/CU15
- Still need Critical and Important security coverage for older servers that remain in operation
- Have already started their migrations to Exchange SE but require additional time to complete the process
What the ESU Program Provides
The program delivers Critical and Important security updates as defined by Microsoft Security Response Center (MSRC) scoring. These updates will be provided privately to ESU customers only – they will not be available through the public Download Center or Windows Update after October 2025.
Key features include:
- Security updates for vulnerabilities rated as Critical or Important
- Private delivery to program participants
- Patch Tuesday notifications confirming whether updates are available
Program Limitations
There are important limitations to consider:
Not a Support Extension: This ESU is explicitly not an extension of the support lifecycle for Exchange 2016/2019. Servers still go out-of-support on October 14, 2025, and customers cannot open support cases unless directly related to ESU security updates.
No Guaranteed Updates: Microsoft is not committing to releasing any security updates during the ESU period. Exchange Server doesn’t necessarily receive updates every Patch Tuesday – updates are only released when Critical or Important security issues are identified.
Limited Duration: The program is valid for exactly 6 months, ending April 14, 2026, with no possibility of extension.
Key Dates to Remember
| Date | Milestone |
| July 1, 2025 | Exchange Server SE became available |
| August 1, 2025 | ESU program becomes available for purchase |
| October 14, 2025 | End-of-support for Exchange 2016 and 2019 |
| April 14, 2026 | ESU program expires (no extensions available) |
Exchange Server SE Migration Path
Exchange Server Subscription Edition (SE) is now generally available and represents the future of on-premises Exchange deployments. Key benefits include:
Modern Lifecycle Policy: Exchange SE follows Microsoft’s Modern Lifecycle Policy, meaning there is no fixed end date for support, provided configurations remain current. The product will be serviced continuously as an evergreen release.
Simplified Upgrades: Exchange SE RTM can be installed as a cumulative update on Exchange Server 2019 CU14 or CU15, making the transition process more straightforward than traditional major version upgrades.
No Feature Changes: Exchange SE RTM has code parity with Exchange 2019 CU15, meaning no significant functional differences at initial release. This reduces migration complexity and training requirements.
Enrollment Process
Organizations interested in the ESU program must contact their Microsoft account team starting August 1, 2025. Account teams will provide information about per-server costs and detailed purchasing instructions. The program operates on a per-server licensing model, requiring organizations to calculate costs based on their current Exchange infrastructure.
Microsoft’s Primary Recommendation
Microsoft strongly emphasizes that organizations should not rely on the ESU program as a long-term solution. The company’s primary recommendation remains migrating to Exchange Subscription Edition (SE) or Exchange Online as quickly as possible.
Since Exchange SE is now available and can be deployed as an in-place upgrade from Exchange 2019, organizations have a clear and supported migration path. Microsoft positions the ESU as a “last resort” option for organizations that absolutely cannot complete their migrations before the October deadline.
Availability Through Other Channels
The announcement focuses exclusively on direct Microsoft account team engagement. While the article doesn’t explicitly address availability through Cloud Solution Providers (CSPs) or other resellers, the emphasis on contacting Microsoft account teams suggests this program may be primarily available through direct Microsoft relationships. Organizations working with partners should verify availability through their existing channels.
Take Action Now
With Exchange Server SE now available and less than three months remaining before the October 14, 2025 end-of-support deadline, IT professionals must act immediately.
- Evaluate your migration timeline: With Exchange SE now released, assess whether your organization can realistically complete its migration before October 14, 2025. The SE upgrade process is designed to be simpler than traditional major version upgrades.
- Start Exchange SE deployment: Begin planning and testing your Exchange SE upgrade immediately. For Exchange 2019 CU14/CU15 environments, this can be done as an in-place upgrade, significantly reducing migration complexity.
- Contact your Microsoft account team: If you cannot complete your Exchange SE migration before the October deadline, reach out to your Microsoft representatives immediately to discuss ESU pricing, requirements, and enrollment procedures.
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